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/*
 * (C) Copyright Taligent, Inc. 1996-1998 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996-1998 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.util;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.time.Instant;
import java.time.ZonedDateTime;
import java.time.temporal.ChronoField;
import sun.util.calendar.BaseCalendar;
import sun.util.calendar.CalendarDate;
import sun.util.calendar.CalendarSystem;
import sun.util.calendar.CalendarUtils;
import sun.util.calendar.Era;
import sun.util.calendar.Gregorian;
import sun.util.calendar.JulianCalendar;
import sun.util.calendar.ZoneInfo;

/**
 * <code>GregorianCalendar</code> is a concrete subclass of
 * <code>Calendar</code> and provides the standard calendar system
 * used by most of the world.
 *
 * <p> <code>GregorianCalendar</code> is a hybrid calendar that
 * supports both the Julian and Gregorian calendar systems with the
 * support of a single discontinuity, which corresponds by default to
 * the Gregorian date when the Gregorian calendar was instituted
 * (October 15, 1582 in some countries, later in others).  The cutover
 * date may be changed by the caller by calling {@link
 * #setGregorianChange(Date) setGregorianChange()}.
 *
 * <p>
 * Historically, in those countries which adopted the Gregorian calendar first,
 * October 4, 1582 (Julian) was thus followed by October 15, 1582 (Gregorian). This calendar models
 * this correctly.  Before the Gregorian cutover, <code>GregorianCalendar</code>
 * implements the Julian calendar.  The only difference between the Gregorian
 * and the Julian calendar is the leap year rule. The Julian calendar specifies
 * leap years every four years, whereas the Gregorian calendar omits century
 * years which are not divisible by 400.
 *
 * <p>
 * <code>GregorianCalendar</code> implements <em>proleptic</em> Gregorian and
 * Julian calendars. That is, dates are computed by extrapolating the current
 * rules indefinitely far backward and forward in time. As a result,
 * <code>GregorianCalendar</code> may be used for all years to generate
 * meaningful and consistent results. However, dates obtained using
 * <code>GregorianCalendar</code> are historically accurate only from March 1, 4
 * AD onward, when modern Julian calendar rules were adopted.  Before this date,
 * leap year rules were applied irregularly, and before 45 BC the Julian
 * calendar did not even exist.
 *
 * <p>
 * Prior to the institution of the Gregorian calendar, New Year's Day was
 * March 25. To avoid confusion, this calendar always uses January 1. A manual
 * adjustment may be made if desired for dates that are prior to the Gregorian
 * changeover and which fall between January 1 and March 24.
 *
 * <h3><a name="week_and_year">Week Of Year and Week Year</a></h3>
 *
 * <p>Values calculated for the {@link Calendar#WEEK_OF_YEAR
 * WEEK_OF_YEAR} field range from 1 to 53. The first week of a
 * calendar year is the earliest seven day period starting on {@link
 * Calendar#getFirstDayOfWeek() getFirstDayOfWeek()} that contains at
 * least {@link Calendar#getMinimalDaysInFirstWeek()
 * getMinimalDaysInFirstWeek()} days from that year. It thus depends
 * on the values of {@code getMinimalDaysInFirstWeek()}, {@code
 * getFirstDayOfWeek()}, and the day of the week of January 1. Weeks
 * between week 1 of one year and week 1 of the following year
 * (exclusive) are numbered sequentially from 2 to 52 or 53 (except
 * for year(s) involved in the Julian-Gregorian transition).
 *
 * <p>The {@code getFirstDayOfWeek()} and {@code
 * getMinimalDaysInFirstWeek()} values are initialized using
 * locale-dependent resources when constructing a {@code
 * GregorianCalendar}. <a name="iso8601_compatible_setting">The week
 * determination is compatible</a> with the ISO 8601 standard when {@code
 * getFirstDayOfWeek()} is {@code MONDAY} and {@code
 * getMinimalDaysInFirstWeek()} is 4, which values are used in locales
 * where the standard is preferred. These values can explicitly be set by
 * calling {@link Calendar#setFirstDayOfWeek(int) setFirstDayOfWeek()} and
 * {@link Calendar#setMinimalDaysInFirstWeek(int)
 * setMinimalDaysInFirstWeek()}.
 *
 * <p>A <a name="week_year"><em>week year</em></a> is in sync with a
 * {@code WEEK_OF_YEAR} cycle. All weeks between the first and last
 * weeks (inclusive) have the same <em>week year</em> value.
 * Therefore, the first and last days of a week year may have
 * different calendar year values.
 *
 * <p>For example, January 1, 1998 is a Thursday. If {@code
 * getFirstDayOfWeek()} is {@code MONDAY} and {@code
 * getMinimalDaysInFirstWeek()} is 4 (ISO 8601 standard compatible
 * setting), then week 1 of 1998 starts on December 29, 1997, and ends
 * on January 4, 1998. The week year is 1998 for the last three days
 * of calendar year 1997. If, however, {@code getFirstDayOfWeek()} is
 * {@code SUNDAY}, then week 1 of 1998 starts on January 4, 1998, and
 * ends on January 10, 1998; the first three days of 1998 then are
 * part of week 53 of 1997 and their week year is 1997.
 *
 * <h4>Week Of Month</h4>
 *
 * <p>Values calculated for the <code>WEEK_OF_MONTH</code> field range from 0
 * to 6.  Week 1 of a month (the days with <code>WEEK_OF_MONTH =
 * 1</code>) is the earliest set of at least
 * <code>getMinimalDaysInFirstWeek()</code> contiguous days in that month,
 * ending on the day before <code>getFirstDayOfWeek()</code>.  Unlike
 * week 1 of a year, week 1 of a month may be shorter than 7 days, need
 * not start on <code>getFirstDayOfWeek()</code>, and will not include days of
 * the previous month.  Days of a month before week 1 have a
 * <code>WEEK_OF_MONTH</code> of 0.
 *
 * <p>For example, if <code>getFirstDayOfWeek()</code> is <code>SUNDAY</code>
 * and <code>getMinimalDaysInFirstWeek()</code> is 4, then the first week of
 * January 1998 is Sunday, January 4 through Saturday, January 10.  These days
 * have a <code>WEEK_OF_MONTH</code> of 1.  Thursday, January 1 through
 * Saturday, January 3 have a <code>WEEK_OF_MONTH</code> of 0.  If
 * <code>getMinimalDaysInFirstWeek()</code> is changed to 3, then January 1
 * through January 3 have a <code>WEEK_OF_MONTH</code> of 1.
 *
 * <h4>Default Fields Values</h4>
 *
 * <p>The <code>clear</code> method sets calendar field(s)
 * undefined. <code>GregorianCalendar</code> uses the following
 * default value for each calendar field if its value is undefined.
 *
 * <table cellpadding="0" cellspacing="3" border="0"
 * summary="GregorianCalendar default field values"
 * style="text-align: left; width: 66%;">
 * <tbody>
 * <tr>
 * <th style="vertical-align: top; background-color: rgb(204, 204, 255);
 * text-align: center;">Field<br>
 * </th>
 * <th style="vertical-align: top; background-color: rgb(204, 204, 255);
 * text-align: center;">Default Value<br>
 * </th>
 * </tr>
 * <tr>
 * <td style="vertical-align: middle;">
 * <code>ERA<br></code>
 * </td>
 * <td style="vertical-align: middle;">
 * <code>AD<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: middle; background-color: rgb(238, 238, 255);">
 * <code>YEAR<br></code>
 * </td>
 * <td style="vertical-align: middle; background-color: rgb(238, 238, 255);">
 * <code>1970<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: middle;">
 * <code>MONTH<br></code>
 * </td>
 * <td style="vertical-align: middle;">
 * <code>JANUARY<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: top; background-color: rgb(238, 238, 255);">
 * <code>DAY_OF_MONTH<br></code>
 * </td>
 * <td style="vertical-align: top; background-color: rgb(238, 238, 255);">
 * <code>1<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: middle;">
 * <code>DAY_OF_WEEK<br></code>
 * </td>
 * <td style="vertical-align: middle;">
 * <code>the first day of week<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: top; background-color: rgb(238, 238, 255);">
 * <code>WEEK_OF_MONTH<br></code>
 * </td>
 * <td style="vertical-align: top; background-color: rgb(238, 238, 255);">
 * <code>0<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: top;">
 * <code>DAY_OF_WEEK_IN_MONTH<br></code>
 * </td>
 * <td style="vertical-align: top;">
 * <code>1<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: middle; background-color: rgb(238, 238, 255);">
 * <code>AM_PM<br></code>
 * </td>
 * <td style="vertical-align: middle; background-color: rgb(238, 238, 255);">
 * <code>AM<br></code>
 * </td>
 * </tr>
 * <tr>
 * <td style="vertical-align: middle;">
 * <code>HOUR, HOUR_OF_DAY, MINUTE, SECOND, MILLISECOND<br></code>
 * </td>
 * <td style="vertical-align: middle;">
 * <code>0<br></code>
 * </td>
 * </tr>
 * </tbody>
 * </table>
 * <br>Default values are not applicable for the fields not listed above.
 *
 * <p>
 * <strong>Example:</strong>
 * <blockquote>
 * <pre>
 * // get the supported ids for GMT-08:00 (Pacific Standard Time)
 * String[] ids = TimeZone.getAvailableIDs(-8 * 60 * 60 * 1000);
 * // if no ids were returned, something is wrong. get out.
 * if (ids.length == 0)
 *     System.exit(0);
 *
 *  // begin output
 * System.out.println("Current Time");
 *
 * // create a Pacific Standard Time time zone
 * SimpleTimeZone pdt = new SimpleTimeZone(-8 * 60 * 60 * 1000, ids[0]);
 *
 * // set up rules for Daylight Saving Time
 * pdt.setStartRule(Calendar.APRIL, 1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 * pdt.setEndRule(Calendar.OCTOBER, -1, Calendar.SUNDAY, 2 * 60 * 60 * 1000);
 *
 * // create a GregorianCalendar with the Pacific Daylight time zone
 * // and the current date and time
 * Calendar calendar = new GregorianCalendar(pdt);
 * Date trialTime = new Date();
 * calendar.setTime(trialTime);
 *
 * // print out a bunch of interesting things
 * System.out.println("ERA: " + calendar.get(Calendar.ERA));
 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 * System.out.println("DATE: " + calendar.get(Calendar.DATE));
 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 * System.out.println("DAY_OF_WEEK_IN_MONTH: "
 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 * System.out.println("ZONE_OFFSET: "
 *                    + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000)));
 * System.out.println("DST_OFFSET: "
 *                    + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000)));
 *
 * System.out.println("Current Time, with hour reset to 3");
 * calendar.clear(Calendar.HOUR_OF_DAY); // so doesn't override
 * calendar.set(Calendar.HOUR, 3);
 * System.out.println("ERA: " + calendar.get(Calendar.ERA));
 * System.out.println("YEAR: " + calendar.get(Calendar.YEAR));
 * System.out.println("MONTH: " + calendar.get(Calendar.MONTH));
 * System.out.println("WEEK_OF_YEAR: " + calendar.get(Calendar.WEEK_OF_YEAR));
 * System.out.println("WEEK_OF_MONTH: " + calendar.get(Calendar.WEEK_OF_MONTH));
 * System.out.println("DATE: " + calendar.get(Calendar.DATE));
 * System.out.println("DAY_OF_MONTH: " + calendar.get(Calendar.DAY_OF_MONTH));
 * System.out.println("DAY_OF_YEAR: " + calendar.get(Calendar.DAY_OF_YEAR));
 * System.out.println("DAY_OF_WEEK: " + calendar.get(Calendar.DAY_OF_WEEK));
 * System.out.println("DAY_OF_WEEK_IN_MONTH: "
 *                    + calendar.get(Calendar.DAY_OF_WEEK_IN_MONTH));
 * System.out.println("AM_PM: " + calendar.get(Calendar.AM_PM));
 * System.out.println("HOUR: " + calendar.get(Calendar.HOUR));
 * System.out.println("HOUR_OF_DAY: " + calendar.get(Calendar.HOUR_OF_DAY));
 * System.out.println("MINUTE: " + calendar.get(Calendar.MINUTE));
 * System.out.println("SECOND: " + calendar.get(Calendar.SECOND));
 * System.out.println("MILLISECOND: " + calendar.get(Calendar.MILLISECOND));
 * System.out.println("ZONE_OFFSET: "
 *        + (calendar.get(Calendar.ZONE_OFFSET)/(60*60*1000))); // in hours
 * System.out.println("DST_OFFSET: "
 *        + (calendar.get(Calendar.DST_OFFSET)/(60*60*1000))); // in hours
 * </pre>
 * </blockquote>
 *
 * @author David Goldsmith, Mark Davis, Chen-Lieh Huang, Alan Liu
 * @see TimeZone
 * @since JDK1.1
 */
public class GregorianCalendar extends Calendar {
    /*
     * Implementation Notes
     *
     * The epoch is the number of days or milliseconds from some defined
     * starting point. The epoch for java.util.Date is used here; that is,
     * milliseconds from January 1, 1970 (Gregorian), midnight UTC.  Other
     * epochs which are used are January 1, year 1 (Gregorian), which is day 1
     * of the Gregorian calendar, and December 30, year 0 (Gregorian), which is
     * day 1 of the Julian calendar.
     *
     * We implement the proleptic Julian and Gregorian calendars.  This means we
     * implement the modern definition of the calendar even though the
     * historical usage differs.  For example, if the Gregorian change is set
     * to new Date(Long.MIN_VALUE), we have a pure Gregorian calendar which
     * labels dates preceding the invention of the Gregorian calendar in 1582 as
     * if the calendar existed then.
     *
     * Likewise, with the Julian calendar, we assume a consistent
     * 4-year leap year rule, even though the historical pattern of
     * leap years is irregular, being every 3 years from 45 BCE
     * through 9 BCE, then every 4 years from 8 CE onwards, with no
     * leap years in-between.  Thus date computations and functions
     * such as isLeapYear() are not intended to be historically
     * accurate.
     */

//////////////////
// Class Variables
//////////////////

  /**
   * Value of the <code>ERA</code> field indicating
   * the period before the common era (before Christ), also known as BCE.
   * The sequence of years at the transition from <code>BC</code> to <code>AD</code> is
   * ..., 2 BC, 1 BC, 1 AD, 2 AD,...
   *
   * @see #ERA
   */
  public static final int BC = 0;

  /**
   * Value of the {@link #ERA} field indicating
   * the period before the common era, the same value as {@link #BC}.
   *
   * @see #CE
   */
  static final int BCE = 0;

  /**
   * Value of the <code>ERA</code> field indicating
   * the common era (Anno Domini), also known as CE.
   * The sequence of years at the transition from <code>BC</code> to <code>AD</code> is
   * ..., 2 BC, 1 BC, 1 AD, 2 AD,...
   *
   * @see #ERA
   */
  public static final int AD = 1;

  /**
   * Value of the {@link #ERA} field indicating
   * the common era, the same value as {@link #AD}.
   *
   * @see #BCE
   */
  static final int CE = 1;

  private static final int EPOCH_OFFSET = 719163; // Fixed date of January 1, 1970 (Gregorian)
  private static final int EPOCH_YEAR = 1970;

  static final int MONTH_LENGTH[]
      = {31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; // 0-based
  static final int LEAP_MONTH_LENGTH[]
      = {31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; // 0-based

  // Useful millisecond constants.  Although ONE_DAY and ONE_WEEK can fit
  // into ints, they must be longs in order to prevent arithmetic overflow
  // when performing (bug 4173516).
  private static final int ONE_SECOND = 1000;
  private static final int ONE_MINUTE = 60 * ONE_SECOND;
  private static final int ONE_HOUR = 60 * ONE_MINUTE;
  private static final long ONE_DAY = 24 * ONE_HOUR;
  private static final long ONE_WEEK = 7 * ONE_DAY;

  /*
   * <pre>
   *                            Greatest       Least
   * Field name        Minimum   Minimum     Maximum     Maximum
   * ----------        -------   -------     -------     -------
   * ERA                     0         0           1           1
   * YEAR                    1         1   292269054   292278994
   * MONTH                   0         0          11          11
   * WEEK_OF_YEAR            1         1          52*         53
   * WEEK_OF_MONTH           0         0           4*          6
   * DAY_OF_MONTH            1         1          28*         31
   * DAY_OF_YEAR             1         1         365*        366
   * DAY_OF_WEEK             1         1           7           7
   * DAY_OF_WEEK_IN_MONTH   -1        -1           4*          6
   * AM_PM                   0         0           1           1
   * HOUR                    0         0          11          11
   * HOUR_OF_DAY             0         0          23          23
   * MINUTE                  0         0          59          59
   * SECOND                  0         0          59          59
   * MILLISECOND             0         0         999         999
   * ZONE_OFFSET        -13:00    -13:00       14:00       14:00
   * DST_OFFSET           0:00      0:00        0:20        2:00
   * </pre>
   * *: depends on the Gregorian change date
   */
  static final int MIN_VALUES[] = {
      BCE,            // ERA
      1,              // YEAR
      JANUARY,        // MONTH
      1,              // WEEK_OF_YEAR
      0,              // WEEK_OF_MONTH
      1,              // DAY_OF_MONTH
      1,              // DAY_OF_YEAR
      SUNDAY,         // DAY_OF_WEEK
      1,              // DAY_OF_WEEK_IN_MONTH
      AM,             // AM_PM
      0,              // HOUR
      0,              // HOUR_OF_DAY
      0,              // MINUTE
      0,              // SECOND
      0,              // MILLISECOND
      -13 * ONE_HOUR,   // ZONE_OFFSET (UNIX compatibility)
      0               // DST_OFFSET
  };
  static final int LEAST_MAX_VALUES[] = {
      CE,             // ERA
      292269054,      // YEAR
      DECEMBER,       // MONTH
      52,             // WEEK_OF_YEAR
      4,              // WEEK_OF_MONTH
      28,             // DAY_OF_MONTH
      365,            // DAY_OF_YEAR
      SATURDAY,       // DAY_OF_WEEK
      4,              // DAY_OF_WEEK_IN
      PM,             // AM_PM
      11,             // HOUR
      23,             // HOUR_OF_DAY
      59,             // MINUTE
      59,             // SECOND
      999,            // MILLISECOND
      14 * ONE_HOUR,    // ZONE_OFFSET
      20 * ONE_MINUTE   // DST_OFFSET (historical least maximum)
  };
  static final int MAX_VALUES[] = {
      CE,             // ERA
      292278994,      // YEAR
      DECEMBER,       // MONTH
      53,             // WEEK_OF_YEAR
      6,              // WEEK_OF_MONTH
      31,             // DAY_OF_MONTH
      366,            // DAY_OF_YEAR
      SATURDAY,       // DAY_OF_WEEK
      6,              // DAY_OF_WEEK_IN
      PM,             // AM_PM
      11,             // HOUR
      23,             // HOUR_OF_DAY
      59,             // MINUTE
      59,             // SECOND
      999,            // MILLISECOND
      14 * ONE_HOUR,    // ZONE_OFFSET
      2 * ONE_HOUR      // DST_OFFSET (double summer time)
  };

  // Proclaim serialization compatibility with JDK 1.1
  @SuppressWarnings("FieldNameHidesFieldInSuperclass")
  static final long serialVersionUID = -8125100834729963327L;

  // Reference to the sun.util.calendar.Gregorian instance (singleton).
  private static final Gregorian gcal =
      CalendarSystem.getGregorianCalendar();

  // Reference to the JulianCalendar instance (singleton), set as needed. See
  // getJulianCalendarSystem().
  private static JulianCalendar jcal;

  // JulianCalendar eras. See getJulianCalendarSystem().
  private static Era[] jeras;

  // The default value of gregorianCutover.
  static final long DEFAULT_GREGORIAN_CUTOVER = -12219292800000L;

/////////////////////
// Instance Variables
/////////////////////

  /**
   * The point at which the Gregorian calendar rules are used, measured in
   * milliseconds from the standard epoch.  Default is October 15, 1582
   * (Gregorian) 00:00:00 UTC or -12219292800000L.  For this value, October 4,
   * 1582 (Julian) is followed by October 15, 1582 (Gregorian).  This
   * corresponds to Julian day number 2299161.
   *
   * @serial
   */
  private long gregorianCutover = DEFAULT_GREGORIAN_CUTOVER;

  /**
   * The fixed date of the gregorianCutover.
   */
  private transient long gregorianCutoverDate =
      (((DEFAULT_GREGORIAN_CUTOVER + 1) / ONE_DAY) - 1) + EPOCH_OFFSET; // == 577736

  /**
   * The normalized year of the gregorianCutover in Gregorian, with
   * 0 representing 1 BCE, -1 representing 2 BCE, etc.
   */
  private transient int gregorianCutoverYear = 1582;

  /**
   * The normalized year of the gregorianCutover in Julian, with 0
   * representing 1 BCE, -1 representing 2 BCE, etc.
   */
  private transient int gregorianCutoverYearJulian = 1582;

  /**
   * gdate always has a sun.util.calendar.Gregorian.Date instance to
   * avoid overhead of creating it. The assumption is that most
   * applications will need only Gregorian calendar calculations.
   */
  private transient BaseCalendar.Date gdate;

  /**
   * Reference to either gdate or a JulianCalendar.Date
   * instance. After calling complete(), this value is guaranteed to
   * be set.
   */
  private transient BaseCalendar.Date cdate;

  /**
   * The CalendarSystem used to calculate the date in cdate. After
   * calling complete(), this value is guaranteed to be set and
   * consistent with the cdate value.
   */
  private transient BaseCalendar calsys;

  /**
   * Temporary int[2] to get time zone offsets. zoneOffsets[0] gets
   * the GMT offset value and zoneOffsets[1] gets the DST saving
   * value.
   */
  private transient int[] zoneOffsets;

  /**
   * Temporary storage for saving original fields[] values in
   * non-lenient mode.
   */
  private transient int[] originalFields;

///////////////
// Constructors
///////////////

  /**
   * Constructs a default <code>GregorianCalendar</code> using the current time
   * in the default time zone with the default
   * {@link Locale.Category#FORMAT FORMAT} locale.
   */
  public GregorianCalendar() {
    this(TimeZone.getDefaultRef(), Locale.getDefault(Locale.Category.FORMAT));
    setZoneShared(true);
  }

  /**
   * Constructs a <code>GregorianCalendar</code> based on the current time
   * in the given time zone with the default
   * {@link Locale.Category#FORMAT FORMAT} locale.
   *
   * @param zone the given time zone.
   */
  public GregorianCalendar(TimeZone zone) {
    this(zone, Locale.getDefault(Locale.Category.FORMAT));
  }

  /**
   * Constructs a <code>GregorianCalendar</code> based on the current time
   * in the default time zone with the given locale.
   *
   * @param aLocale the given locale.
   */
  public GregorianCalendar(Locale aLocale) {
    this(TimeZone.getDefaultRef(), aLocale);
    setZoneShared(true);
  }

  /**
   * Constructs a <code>GregorianCalendar</code> based on the current time
   * in the given time zone with the given locale.
   *
   * @param zone the given time zone.
   * @param aLocale the given locale.
   */
  public GregorianCalendar(TimeZone zone, Locale aLocale) {
    super(zone, aLocale);
    gdate = (BaseCalendar.Date) gcal.newCalendarDate(zone);
    setTimeInMillis(System.currentTimeMillis());
  }

  /**
   * Constructs a <code>GregorianCalendar</code> with the given date set
   * in the default time zone with the default locale.
   *
   * @param year the value used to set the <code>YEAR</code> calendar field in the calendar.
   * @param month the value used to set the <code>MONTH</code> calendar field in the calendar. Month
   * value is 0-based. e.g., 0 for January.
   * @param dayOfMonth the value used to set the <code>DAY_OF_MONTH</code> calendar field in the
   * calendar.
   */
  public GregorianCalendar(int year, int month, int dayOfMonth) {
    this(year, month, dayOfMonth, 0, 0, 0, 0);
  }

  /**
   * Constructs a <code>GregorianCalendar</code> with the given date
   * and time set for the default time zone with the default locale.
   *
   * @param year the value used to set the <code>YEAR</code> calendar field in the calendar.
   * @param month the value used to set the <code>MONTH</code> calendar field in the calendar. Month
   * value is 0-based. e.g., 0 for January.
   * @param dayOfMonth the value used to set the <code>DAY_OF_MONTH</code> calendar field in the
   * calendar.
   * @param hourOfDay the value used to set the <code>HOUR_OF_DAY</code> calendar field in the
   * calendar.
   * @param minute the value used to set the <code>MINUTE</code> calendar field in the calendar.
   */
  public GregorianCalendar(int year, int month, int dayOfMonth, int hourOfDay,
      int minute) {
    this(year, month, dayOfMonth, hourOfDay, minute, 0, 0);
  }

  /**
   * Constructs a GregorianCalendar with the given date
   * and time set for the default time zone with the default locale.
   *
   * @param year the value used to set the <code>YEAR</code> calendar field in the calendar.
   * @param month the value used to set the <code>MONTH</code> calendar field in the calendar. Month
   * value is 0-based. e.g., 0 for January.
   * @param dayOfMonth the value used to set the <code>DAY_OF_MONTH</code> calendar field in the
   * calendar.
   * @param hourOfDay the value used to set the <code>HOUR_OF_DAY</code> calendar field in the
   * calendar.
   * @param minute the value used to set the <code>MINUTE</code> calendar field in the calendar.
   * @param second the value used to set the <code>SECOND</code> calendar field in the calendar.
   */
  public GregorianCalendar(int year, int month, int dayOfMonth, int hourOfDay,
      int minute, int second) {
    this(year, month, dayOfMonth, hourOfDay, minute, second, 0);
  }

  /**
   * Constructs a <code>GregorianCalendar</code> with the given date
   * and time set for the default time zone with the default locale.
   *
   * @param year the value used to set the <code>YEAR</code> calendar field in the calendar.
   * @param month the value used to set the <code>MONTH</code> calendar field in the calendar. Month
   * value is 0-based. e.g., 0 for January.
   * @param dayOfMonth the value used to set the <code>DAY_OF_MONTH</code> calendar field in the
   * calendar.
   * @param hourOfDay the value used to set the <code>HOUR_OF_DAY</code> calendar field in the
   * calendar.
   * @param minute the value used to set the <code>MINUTE</code> calendar field in the calendar.
   * @param second the value used to set the <code>SECOND</code> calendar field in the calendar.
   * @param millis the value used to set the <code>MILLISECOND</code> calendar field
   */
  GregorianCalendar(int year, int month, int dayOfMonth,
      int hourOfDay, int minute, int second, int millis) {
    super();
    gdate = (BaseCalendar.Date) gcal.newCalendarDate(getZone());
    this.set(YEAR, year);
    this.set(MONTH, month);
    this.set(DAY_OF_MONTH, dayOfMonth);

    // Set AM_PM and HOUR here to set their stamp values before
    // setting HOUR_OF_DAY (6178071).
    if (hourOfDay >= 12 && hourOfDay <= 23) {
      // If hourOfDay is a valid PM hour, set the correct PM values
      // so that it won't throw an exception in case it's set to
      // non-lenient later.
      this.internalSet(AM_PM, PM);
      this.internalSet(HOUR, hourOfDay - 12);
    } else {
      // The default value for AM_PM is AM.
      // We don't care any out of range value here for leniency.
      this.internalSet(HOUR, hourOfDay);
    }
    // The stamp values of AM_PM and HOUR must be COMPUTED. (6440854)
    setFieldsComputed(HOUR_MASK | AM_PM_MASK);

    this.set(HOUR_OF_DAY, hourOfDay);
    this.set(MINUTE, minute);
    this.set(SECOND, second);
    // should be changed to set() when this constructor is made
    // public.
    this.internalSet(MILLISECOND, millis);
  }

  /**
   * Constructs an empty GregorianCalendar.
   *
   * @param zone the given time zone
   * @param aLocale the given locale
   * @param flag the flag requesting an empty instance
   */
  GregorianCalendar(TimeZone zone, Locale locale, boolean flag) {
    super(zone, locale);
    gdate = (BaseCalendar.Date) gcal.newCalendarDate(getZone());
  }

/////////////////
// Public methods
/////////////////

  /**
   * Sets the <code>GregorianCalendar</code> change date. This is the point when the switch
   * from Julian dates to Gregorian dates occurred. Default is October 15,
   * 1582 (Gregorian). Previous to this, dates will be in the Julian calendar.
   * <p>
   * To obtain a pure Julian calendar, set the change date to
   * <code>Date(Long.MAX_VALUE)</code>.  To obtain a pure Gregorian calendar,
   * set the change date to <code>Date(Long.MIN_VALUE)</code>.
   *
   * @param date the given Gregorian cutover date.
   */
  public void setGregorianChange(Date date) {
    long cutoverTime = date.getTime();
    if (cutoverTime == gregorianCutover) {
      return;
    }
    // Before changing the cutover date, make sure to have the
    // time of this calendar.
    complete();
    setGregorianChange(cutoverTime);
  }

  private void setGregorianChange(long cutoverTime) {
    gregorianCutover = cutoverTime;
    gregorianCutoverDate = CalendarUtils.floorDivide(cutoverTime, ONE_DAY)
        + EPOCH_OFFSET;

    // To provide the "pure" Julian calendar as advertised.
    // Strictly speaking, the last millisecond should be a
    // Gregorian date. However, the API doc specifies that setting
    // the cutover date to Long.MAX_VALUE will make this calendar
    // a pure Julian calendar. (See 4167995)
    if (cutoverTime == Long.MAX_VALUE) {
      gregorianCutoverDate++;
    }

    BaseCalendar.Date d = getGregorianCutoverDate();

    // Set the cutover year (in the Gregorian year numbering)
    gregorianCutoverYear = d.getYear();

    BaseCalendar julianCal = getJulianCalendarSystem();
    d = (BaseCalendar.Date) julianCal.newCalendarDate(TimeZone.NO_TIMEZONE);
    julianCal.getCalendarDateFromFixedDate(d, gregorianCutoverDate - 1);
    gregorianCutoverYearJulian = d.getNormalizedYear();

    if (time < gregorianCutover) {
      // The field values are no longer valid under the new
      // cutover date.
      setUnnormalized();
    }
  }

  /**
   * Gets the Gregorian Calendar change date.  This is the point when the
   * switch from Julian dates to Gregorian dates occurred. Default is
   * October 15, 1582 (Gregorian). Previous to this, dates will be in the Julian
   * calendar.
   *
   * @return the Gregorian cutover date for this <code>GregorianCalendar</code> object.
   */
  public final Date getGregorianChange() {
    return new Date(gregorianCutover);
  }

  /**
   * Determines if the given year is a leap year. Returns <code>true</code> if
   * the given year is a leap year. To specify BC year numbers,
   * <code>1 - year number</code> must be given. For example, year BC 4 is
   * specified as -3.
   *
   * @param year the given year.
   * @return <code>true</code> if the given year is a leap year; <code>false</code> otherwise.
   */
  public boolean isLeapYear(int year) {
    if ((year & 3) != 0) {
      return false;
    }

    if (year > gregorianCutoverYear) {
      return (year % 100 != 0) || (year % 400 == 0); // Gregorian
    }
    if (year < gregorianCutoverYearJulian) {
      return true; // Julian
    }
    boolean gregorian;
    // If the given year is the Gregorian cutover year, we need to
    // determine which calendar system to be applied to February in the year.
    if (gregorianCutoverYear == gregorianCutoverYearJulian) {
      BaseCalendar.Date d = getCalendarDate(gregorianCutoverDate); // Gregorian
      gregorian = d.getMonth() < BaseCalendar.MARCH;
    } else {
      gregorian = year == gregorianCutoverYear;
    }
    return gregorian ? (year % 100 != 0) || (year % 400 == 0) : true;
  }

  /**
   * Returns {@code "gregory"} as the calendar type.
   *
   * @return {@code "gregory"}
   * @since 1.8
   */
  @Override
  public String getCalendarType() {
    return "gregory";
  }

  /**
   * Compares this <code>GregorianCalendar</code> to the specified
   * <code>Object</code>. The result is <code>true</code> if and
   * only if the argument is a <code>GregorianCalendar</code> object
   * that represents the same time value (millisecond offset from
   * the <a href="Calendar.html#Epoch">Epoch</a>) under the same
   * <code>Calendar</code> parameters and Gregorian change date as
   * this object.
   *
   * @param obj the object to compare with.
   * @return <code>true</code> if this object is equal to <code>obj</code>; <code>false</code>
   * otherwise.
   * @see Calendar#compareTo(Calendar)
   */
  @Override
  public boolean equals(Object obj) {
    return obj instanceof GregorianCalendar &&
        super.equals(obj) &&
        gregorianCutover == ((GregorianCalendar) obj).gregorianCutover;
  }

  /**
   * Generates the hash code for this <code>GregorianCalendar</code> object.
   */
  @Override
  public int hashCode() {
    return super.hashCode() ^ (int) gregorianCutoverDate;
  }

  /**
   * Adds the specified (signed) amount of time to the given calendar field,
   * based on the calendar's rules.
   *
   * <p><em>Add rule 1</em>. The value of <code>field</code>
   * after the call minus the value of <code>field</code> before the
   * call is <code>amount</code>, modulo any overflow that has occurred in
   * <code>field</code>. Overflow occurs when a field value exceeds its
   * range and, as a result, the next larger field is incremented or
   * decremented and the field value is adjusted back into its range.</p>
   *
   * <p><em>Add rule 2</em>. If a smaller field is expected to be
   * invariant, but it is impossible for it to be equal to its
   * prior value because of changes in its minimum or maximum after
   * <code>field</code> is changed, then its value is adjusted to be as close
   * as possible to its expected value. A smaller field represents a
   * smaller unit of time. <code>HOUR</code> is a smaller field than
   * <code>DAY_OF_MONTH</code>. No adjustment is made to smaller fields
   * that are not expected to be invariant. The calendar system
   * determines what fields are expected to be invariant.</p>
   *
   * @param field the calendar field.
   * @param amount the amount of date or time to be added to the field.
   * @throws IllegalArgumentException if <code>field</code> is <code>ZONE_OFFSET</code>,
   * <code>DST_OFFSET</code>, or unknown, or if any calendar fields have out-of-range values in
   * non-lenient mode.
   */
  @Override
  public void add(int field, int amount) {
    // If amount == 0, do nothing even the given field is out of
    // range. This is tested by JCK.
    if (amount == 0) {
      return;   // Do nothing!
    }

    if (field < 0 || field >= ZONE_OFFSET) {
      throw new IllegalArgumentException();
    }

    // Sync the time and calendar fields.
    complete();

    if (field == YEAR) {
      int year = internalGet(YEAR);
      if (internalGetEra() == CE) {
        year += amount;
        if (year > 0) {
          set(YEAR, year);
        } else { // year <= 0
          set(YEAR, 1 - year);
          // if year == 0, you get 1 BCE.
          set(ERA, BCE);
        }
      } else { // era == BCE
        year -= amount;
        if (year > 0) {
          set(YEAR, year);
        } else { // year <= 0
          set(YEAR, 1 - year);
          // if year == 0, you get 1 CE
          set(ERA, CE);
        }
      }
      pinDayOfMonth();
    } else if (field == MONTH) {
      int month = internalGet(MONTH) + amount;
      int year = internalGet(YEAR);
      int y_amount;

      if (month >= 0) {
        y_amount = month / 12;
      } else {
        y_amount = (month + 1) / 12 - 1;
      }
      if (y_amount != 0) {
        if (internalGetEra() == CE) {
          year += y_amount;
          if (year > 0) {
            set(YEAR, year);
          } else { // year <= 0
            set(YEAR, 1 - year);
            // if year == 0, you get 1 BCE
            set(ERA, BCE);
          }
        } else { // era == BCE
          year -= y_amount;
          if (year > 0) {
            set(YEAR, year);
          } else { // year <= 0
            set(YEAR, 1 - year);
            // if year == 0, you get 1 CE
            set(ERA, CE);
          }
        }
      }

      if (month >= 0) {
        set(MONTH, month % 12);
      } else {
        // month < 0
        month %= 12;
        if (month < 0) {
          month += 12;
        }
        set(MONTH, JANUARY + month);
      }
      pinDayOfMonth();
    } else if (field == ERA) {
      int era = internalGet(ERA) + amount;
      if (era < 0) {
        era = 0;
      }
      if (era > 1) {
        era = 1;
      }
      set(ERA, era);
    } else {
      long delta = amount;
      long timeOfDay = 0;
      switch (field) {
        // Handle the time fields here. Convert the given
        // amount to milliseconds and call setTimeInMillis.
        case HOUR:
        case HOUR_OF_DAY:
          delta *= 60 * 60 * 1000;        // hours to minutes
          break;

        case MINUTE:
          delta *= 60 * 1000;             // minutes to seconds
          break;

        case SECOND:
          delta *= 1000;                  // seconds to milliseconds
          break;

        case MILLISECOND:
          break;

        // Handle week, day and AM_PM fields which involves
        // time zone offset change adjustment. Convert the
        // given amount to the number of days.
        case WEEK_OF_YEAR:
        case WEEK_OF_MONTH:
        case DAY_OF_WEEK_IN_MONTH:
          delta *= 7;
          break;

        case DAY_OF_MONTH: // synonym of DATE
        case DAY_OF_YEAR:
        case DAY_OF_WEEK:
          break;

        case AM_PM:
          // Convert the amount to the number of days (delta)
          // and +12 or -12 hours (timeOfDay).
          delta = amount / 2;
          timeOfDay = 12 * (amount % 2);
          break;
      }

      // The time fields don't require time zone offset change
      // adjustment.
      if (field >= HOUR) {
        setTimeInMillis(time + delta);
        return;
      }

      // The rest of the fields (week, day or AM_PM fields)
      // require time zone offset (both GMT and DST) change
      // adjustment.

      // Translate the current time to the fixed date and time
      // of the day.
      long fd = getCurrentFixedDate();
      timeOfDay += internalGet(HOUR_OF_DAY);
      timeOfDay *= 60;
      timeOfDay += internalGet(MINUTE);
      timeOfDay *= 60;
      timeOfDay += internalGet(SECOND);
      timeOfDay *= 1000;
      timeOfDay += internalGet(MILLISECOND);
      if (timeOfDay >= ONE_DAY) {
        fd++;
        timeOfDay -= ONE_DAY;
      } else if (timeOfDay < 0) {
        fd--;
        timeOfDay += ONE_DAY;
      }

      fd += delta; // fd is the expected fixed date after the calculation
      int zoneOffset = internalGet(ZONE_OFFSET) + internalGet(DST_OFFSET);
      setTimeInMillis((fd - EPOCH_OFFSET) * ONE_DAY + timeOfDay - zoneOffset);
      zoneOffset -= internalGet(ZONE_OFFSET) + internalGet(DST_OFFSET);
      // If the time zone offset has changed, then adjust the difference.
      if (zoneOffset != 0) {
        setTimeInMillis(time + zoneOffset);
        long fd2 = getCurrentFixedDate();
        // If the adjustment has changed the date, then take
        // the previous one.
        if (fd2 != fd) {
          setTimeInMillis(time - zoneOffset);
        }
      }
    }
  }

  /**
   * Adds or subtracts (up/down) a single unit of time on the given time field without changing
   * larger fields. <p> <em>Example</em>: Consider a <code>GregorianCalendar</code> originally set
   * to December 31, 1999. Calling {@link #roll(int, boolean) roll(Calendar.MONTH, true)} sets the
   * calendar to January 31, 1999.  The <code>YEAR</code> field is unchanged because it is a larger
   * field than <code>MONTH</code>.</p>
   *
   * @param up indicates if the value of the specified calendar field is to be rolled up or rolled
   * down. Use <code>true</code> if rolling up, <code>false</code> otherwise.
   * @throws IllegalArgumentException if <code>field</code> is <code>ZONE_OFFSET</code>,
   * <code>DST_OFFSET</code>, or unknown, or if any calendar fields have out-of-range values in
   * non-lenient mode.
   * @see #add(int, int)
   * @see #set(int, int)
   */
  @Override
  public void roll(int field, boolean up) {
    roll(field, up ? +1 : -1);
  }

  /**
   * Adds a signed amount to the specified calendar field without changing larger fields.
   * A negative roll amount means to subtract from field without changing
   * larger fields. If the specified amount is 0, this method performs nothing.
   *
   * <p>This method calls {@link #complete()} before adding the
   * amount so that all the calendar fields are normalized. If there
   * is any calendar field having an out-of-range value in non-lenient mode, then an
   * <code>IllegalArgumentException</code> is thrown.
   *
   * <p>
   * <em>Example</em>: Consider a <code>GregorianCalendar</code>
   * originally set to August 31, 1999. Calling <code>roll(Calendar.MONTH,
   * 8)</code> sets the calendar to April 30, <strong>1999</strong>. Using a
   * <code>GregorianCalendar</code>, the <code>DAY_OF_MONTH</code> field cannot
   * be 31 in the month April. <code>DAY_OF_MONTH</code> is set to the closest possible
   * value, 30. The <code>YEAR</code> field maintains the value of 1999 because it
   * is a larger field than <code>MONTH</code>.
   * <p>
   * <em>Example</em>: Consider a <code>GregorianCalendar</code>
   * originally set to Sunday June 6, 1999. Calling
   * <code>roll(Calendar.WEEK_OF_MONTH, -1)</code> sets the calendar to
   * Tuesday June 1, 1999, whereas calling
   * <code>add(Calendar.WEEK_OF_MONTH, -1)</code> sets the calendar to
   * Sunday May 30, 1999. This is because the roll rule imposes an
   * additional constraint: The <code>MONTH</code> must not change when the
   * <code>WEEK_OF_MONTH</code> is rolled. Taken together with add rule 1,
   * the resultant date must be between Tuesday June 1 and Saturday June
   * 5. According to add rule 2, the <code>DAY_OF_WEEK</code>, an invariant
   * when changing the <code>WEEK_OF_MONTH</code>, is set to Tuesday, the
   * closest possible value to Sunday (where Sunday is the first day of the
   * week).</p>
   *
   * @param field the calendar field.
   * @param amount the signed amount to add to <code>field</code>.
   * @throws IllegalArgumentException if <code>field</code> is <code>ZONE_OFFSET</code>,
   * <code>DST_OFFSET</code>, or unknown, or if any calendar fields have out-of-range values in
   * non-lenient mode.
   * @see #roll(int, boolean)
   * @see #add(int, int)
   * @see #set(int, int)
   * @since 1.2
   */
  @Override
  public void roll(int field, int amount) {
    // If amount == 0, do nothing even the given field is out of
    // range. This is tested by JCK.
    if (amount == 0) {
      return;
    }

    if (field < 0 || field >= ZONE_OFFSET) {
      throw new IllegalArgumentException();
    }

    // Sync the time and calendar fields.
    complete();

    int min = getMinimum(field);
    int max = getMaximum(field);

    switch (field) {
      case AM_PM:
      case ERA:
      case YEAR:
      case MINUTE:
      case SECOND:
      case MILLISECOND:
        // These fields are handled simply, since they have fixed minima
        // and maxima.  The field DAY_OF_MONTH is almost as simple.  Other
        // fields are complicated, since the range within they must roll
        // varies depending on the date.
        break;

      case HOUR:
      case HOUR_OF_DAY: {
        int unit = max + 1; // 12 or 24 hours
        int h = internalGet(field);
        int nh = (h + amount) % unit;
        if (nh < 0) {
          nh += unit;
        }
        time += ONE_HOUR * (nh - h);

        // The day might have changed, which could happen if
        // the daylight saving time transition brings it to
        // the next day, although it's very unlikely. But we
        // have to make sure not to change the larger fields.
        CalendarDate d = calsys.getCalendarDate(time, getZone());
        if (internalGet(DAY_OF_MONTH) != d.getDayOfMonth()) {
          d.setDate(internalGet(YEAR),
              internalGet(MONTH) + 1,
              internalGet(DAY_OF_MONTH));
          if (field == HOUR) {
            assert (internalGet(AM_PM) == PM);
            d.addHours(+12); // restore PM
          }
          time = calsys.getTime(d);
        }
        int hourOfDay = d.getHours();
        internalSet(field, hourOfDay % unit);
        if (field == HOUR) {
          internalSet(HOUR_OF_DAY, hourOfDay);
        } else {
          internalSet(AM_PM, hourOfDay / 12);
          internalSet(HOUR, hourOfDay % 12);
        }

        // Time zone offset and/or daylight saving might have changed.
        int zoneOffset = d.getZoneOffset();
        int saving = d.getDaylightSaving();
        internalSet(ZONE_OFFSET, zoneOffset - saving);
        internalSet(DST_OFFSET, saving);
        return;
      }

      case MONTH:
        // Rolling the month involves both pinning the final value to [0, 11]
        // and adjusting the DAY_OF_MONTH if necessary.  We only adjust the
        // DAY_OF_MONTH if, after updating the MONTH field, it is illegal.
        // E.g., <jan31>.roll(MONTH, 1) -> <feb28> or <feb29>.
      {
        if (!isCutoverYear(cdate.getNormalizedYear())) {
          int mon = (internalGet(MONTH) + amount) % 12;
          if (mon < 0) {
            mon += 12;
          }
          set(MONTH, mon);

          // Keep the day of month in the range.  We don't want to spill over
          // into the next month; e.g., we don't want jan31 + 1 mo -> feb31 ->
          // mar3.
          int monthLen = monthLength(mon);
          if (internalGet(DAY_OF_MONTH) > monthLen) {
            set(DAY_OF_MONTH, monthLen);
          }
        } else {
          // We need to take care of different lengths in
          // year and month due to the cutover.
          int yearLength = getActualMaximum(MONTH) + 1;
          int mon = (internalGet(MONTH) + amount) % yearLength;
          if (mon < 0) {
            mon += yearLength;
          }
          set(MONTH, mon);
          int monthLen = getActualMaximum(DAY_OF_MONTH);
          if (internalGet(DAY_OF_MONTH) > monthLen) {
            set(DAY_OF_MONTH, monthLen);
          }
        }
        return;
      }

      case WEEK_OF_YEAR: {
        int y = cdate.getNormalizedYear();
        max = getActualMaximum(WEEK_OF_YEAR);
        set(DAY_OF_WEEK, internalGet(DAY_OF_WEEK));
        int woy = internalGet(WEEK_OF_YEAR);
        int value = woy + amount;
        if (!isCutoverYear(y)) {
          int weekYear = getWeekYear();
          if (weekYear == y) {
            // If the new value is in between min and max
            // (exclusive), then we can use the value.
            if (value > min && value < max) {
              set(WEEK_OF_YEAR, value);
              return;
            }
            long fd = getCurrentFixedDate();
            // Make sure that the min week has the current DAY_OF_WEEK
            // in the calendar year
            long day1 = fd - (7 * (woy - min));
            if (calsys.getYearFromFixedDate(day1) != y) {
              min++;
            }

            // Make sure the same thing for the max week
            fd += 7 * (max - internalGet(WEEK_OF_YEAR));
            if (calsys.getYearFromFixedDate(fd) != y) {
              max--;
            }
          } else {
            // When WEEK_OF_YEAR and YEAR are out of sync,
            // adjust woy and amount to stay in the calendar year.
            if (weekYear > y) {
              if (amount < 0) {
                amount++;
              }
              woy = max;
            } else {
              if (amount > 0) {
                amount -= woy - max;
              }
              woy = min;
            }
          }
          set(field, getRolledValue(woy, amount, min, max));
          return;
        }

        // Handle cutover here.
        long fd = getCurrentFixedDate();
        BaseCalendar cal;
        if (gregorianCutoverYear == gregorianCutoverYearJulian) {
          cal = getCutoverCalendarSystem();
        } else if (y == gregorianCutoverYear) {
          cal = gcal;
        } else {
          cal = getJulianCalendarSystem();
        }
        long day1 = fd - (7 * (woy - min));
        // Make sure that the min week has the current DAY_OF_WEEK
        if (cal.getYearFromFixedDate(day1) != y) {
          min++;
        }

        // Make sure the same thing for the max week
        fd += 7 * (max - woy);
        cal = (fd >= gregorianCutoverDate) ? gcal : getJulianCalendarSystem();
        if (cal.getYearFromFixedDate(fd) != y) {
          max--;
        }
        // value: the new WEEK_OF_YEAR which must be converted
        // to month and day of month.
        value = getRolledValue(woy, amount, min, max) - 1;
        BaseCalendar.Date d = getCalendarDate(day1 + value * 7);
        set(MONTH, d.getMonth() - 1);
        set(DAY_OF_MONTH, d.getDayOfMonth());
        return;
      }

      case WEEK_OF_MONTH: {
        boolean isCutoverYear = isCutoverYear(cdate.getNormalizedYear());
        // dow: relative day of week from first day of week
        int dow = internalGet(DAY_OF_WEEK) - getFirstDayOfWeek();
        if (dow < 0) {
          dow += 7;
        }

        long fd = getCurrentFixedDate();
        long month1;     // fixed date of the first day (usually 1) of the month
        int monthLength; // actual month length
        if (isCutoverYear) {
          month1 = getFixedDateMonth1(cdate, fd);
          monthLength = actualMonthLength();
        } else {
          month1 = fd - internalGet(DAY_OF_MONTH) + 1;
          monthLength = calsys.getMonthLength(cdate);
        }

        // the first day of week of the month.
        long monthDay1st = BaseCalendar.getDayOfWeekDateOnOrBefore(month1 + 6,
            getFirstDayOfWeek());
        // if the week has enough days to form a week, the
        // week starts from the previous month.
        if ((int) (monthDay1st - month1) >= getMinimalDaysInFirstWeek()) {
          monthDay1st -= 7;
        }
        max = getActualMaximum(field);

        // value: the new WEEK_OF_MONTH value
        int value = getRolledValue(internalGet(field), amount, 1, max) - 1;

        // nfd: fixed date of the rolled date
        long nfd = monthDay1st + value * 7 + dow;

        // Unlike WEEK_OF_YEAR, we need to change day of week if the
        // nfd is out of the month.
        if (nfd < month1) {
          nfd = month1;
        } else if (nfd >= (month1 + monthLength)) {
          nfd = month1 + monthLength - 1;
        }
        int dayOfMonth;
        if (isCutoverYear) {
          // If we are in the cutover year, convert nfd to
          // its calendar date and use dayOfMonth.
          BaseCalendar.Date d = getCalendarDate(nfd);
          dayOfMonth = d.getDayOfMonth();
        } else {
          dayOfMonth = (int) (nfd - month1) + 1;
        }
        set(DAY_OF_MONTH, dayOfMonth);
        return;
      }

      case DAY_OF_MONTH: {
        if (!isCutoverYear(cdate.getNormalizedYear())) {
          max = calsys.getMonthLength(cdate);
          break;
        }

        // Cutover year handling
        long fd = getCurrentFixedDate();
        long month1 = getFixedDateMonth1(cdate, fd);
        // It may not be a regular month. Convert the date and range to
        // the relative values, perform the roll, and
        // convert the result back to the rolled date.
        int value = getRolledValue((int) (fd - month1), amount, 0, actualMonthLength() - 1);
        BaseCalendar.Date d = getCalendarDate(month1 + value);
        assert d.getMonth() - 1 == internalGet(MONTH);
        set(DAY_OF_MONTH, d.getDayOfMonth());
        return;
      }

      case DAY_OF_YEAR: {
        max = getActualMaximum(field);
        if (!isCutoverYear(cdate.getNormalizedYear())) {
          break;
        }

        // Handle cutover here.
        long fd = getCurrentFixedDate();
        long jan1 = fd - internalGet(DAY_OF_YEAR) + 1;
        int value = getRolledValue((int) (fd - jan1) + 1, amount, min, max);
        BaseCalendar.Date d = getCalendarDate(jan1 + value - 1);
        set(MONTH, d.getMonth() - 1);
        set(DAY_OF_MONTH, d.getDayOfMonth());
        return;
      }

      case DAY_OF_WEEK: {
        if (!isCutoverYear(cdate.getNormalizedYear())) {
          // If the week of year is in the same year, we can
          // just change DAY_OF_WEEK.
          int weekOfYear = internalGet(WEEK_OF_YEAR);
          if (weekOfYear > 1 && weekOfYear < 52) {
            set(WEEK_OF_YEAR, weekOfYear); // update stamp[WEEK_OF_YEAR]
            max = SATURDAY;
            break;
          }
        }

        // We need to handle it in a different way around year
        // boundaries and in the cutover year. Note that
        // changing era and year values violates the roll
        // rule: not changing larger calendar fields...
        amount %= 7;
        if (amount == 0) {
          return;
        }
        long fd = getCurrentFixedDate();
        long dowFirst = BaseCalendar.getDayOfWeekDateOnOrBefore(fd, getFirstDayOfWeek());
        fd += amount;
        if (fd < dowFirst) {
          fd += 7;
        } else if (fd >= dowFirst + 7) {
          fd -= 7;
        }
        BaseCalendar.Date d = getCalendarDate(fd);
        set(ERA, (d.getNormalizedYear() <= 0 ? BCE : CE));
        set(d.getYear(), d.getMonth() - 1, d.getDayOfMonth());
        return;
      }

      case DAY_OF_WEEK_IN_MONTH: {
        min = 1; // after normalized, min should be 1.
        if (!isCutoverYear(cdate.getNormalizedYear())) {
          int dom = internalGet(DAY_OF_MONTH);
          int monthLength = calsys.getMonthLength(cdate);
          int lastDays = monthLength % 7;
          max = monthLength / 7;
          int x = (dom - 1) % 7;
          if (x < lastDays) {
            max++;
          }
          set(DAY_OF_WEEK, internalGet(DAY_OF_WEEK));
          break;
        }

        // Cutover year handling
        long fd = getCurrentFixedDate();
        long month1 = getFixedDateMonth1(cdate, fd);
        int monthLength = actualMonthLength();
        int lastDays = monthLength % 7;
        max = monthLength / 7;
        int x = (int) (fd - month1) % 7;
        if (x < lastDays) {
          max++;
        }
        int value = getRolledValue(internalGet(field), amount, min, max) - 1;
        fd = month1 + value * 7 + x;
        BaseCalendar cal = (fd >= gregorianCutoverDate) ? gcal : getJulianCalendarSystem();
        BaseCalendar.Date d = (BaseCalendar.Date) cal.newCalendarDate(TimeZone.NO_TIMEZONE);
        cal.getCalendarDateFromFixedDate(d, fd);
        set(DAY_OF_MONTH, d.getDayOfMonth());
        return;
      }
    }

    set(field, getRolledValue(internalGet(field), amount, min, max));
  }

  /**
   * Returns the minimum value for the given calendar field of this
   * <code>GregorianCalendar</code> instance. The minimum value is
   * defined as the smallest value returned by the {@link
   * Calendar#get(int) get} method for any possible time value,
   * taking into consideration the current values of the
   * {@link Calendar#getFirstDayOfWeek() getFirstDayOfWeek},
   * {@link Calendar#getMinimalDaysInFirstWeek() getMinimalDaysInFirstWeek},
   * {@link #getGregorianChange() getGregorianChange} and
   * {@link Calendar#getTimeZone() getTimeZone} methods.
   *
   * @param field the calendar field.
   * @return the minimum value for the given calendar field.
   * @see #getMaximum(int)
   * @see #getGreatestMinimum(int)
   * @see #getLeastMaximum(int)
   * @see #getActualMinimum(int)
   * @see #getActualMaximum(int)
   */
  @Override
  public int getMinimum(int field) {
    return MIN_VALUES[field];
  }

  /**
   * Returns the maximum value for the given calendar field of this
   * <code>GregorianCalendar</code> instance. The maximum value is
   * defined as the largest value returned by the {@link
   * Calendar#get(int) get} method for any possible time value,
   * taking into consideration the current values of the
   * {@link Calendar#getFirstDayOfWeek() getFirstDayOfWeek},
   * {@link Calendar#getMinimalDaysInFirstWeek() getMinimalDaysInFirstWeek},
   * {@link #getGregorianChange() getGregorianChange} and
   * {@link Calendar#getTimeZone() getTimeZone} methods.
   *
   * @param field the calendar field.
   * @return the maximum value for the given calendar field.
   * @see #getMinimum(int)
   * @see #getGreatestMinimum(int)
   * @see #getLeastMaximum(int)
   * @see #getActualMinimum(int)
   * @see #getActualMaximum(int)
   */
  @Override
  public int getMaximum(int field) {
    switch (field) {
      case MONTH:
      case DAY_OF_MONTH:
      case DAY_OF_YEAR:
      case WEEK_OF_YEAR:
      case WEEK_OF_MONTH:
      case DAY_OF_WEEK_IN_MONTH:
      case YEAR: {
        // On or after Gregorian 200-3-1, Julian and Gregorian
        // calendar dates are the same or Gregorian dates are
        // larger (i.e., there is a "gap") after 300-3-1.
        if (gregorianCutoverYear > 200) {
          break;
        }
        // There might be "overlapping" dates.
        GregorianCalendar gc = (GregorianCalendar) clone();
        gc.setLenient(true);
        gc.setTimeInMillis(gregorianCutover);
        int v1 = gc.getActualMaximum(field);
        gc.setTimeInMillis(gregorianCutover - 1);
        int v2 = gc.getActualMaximum(field);
        return Math.max(MAX_VALUES[field], Math.max(v1, v2));
      }
    }
    return MAX_VALUES[field];
  }

  /**
   * Returns the highest minimum value for the given calendar field
   * of this <code>GregorianCalendar</code> instance. The highest
   * minimum value is defined as the largest value returned by
   * {@link #getActualMinimum(int)} for any possible time value,
   * taking into consideration the current values of the
   * {@link Calendar#getFirstDayOfWeek() getFirstDayOfWeek},
   * {@link Calendar#getMinimalDaysInFirstWeek() getMinimalDaysInFirstWeek},
   * {@link #getGregorianChange() getGregorianChange} and
   * {@link Calendar#getTimeZone() getTimeZone} methods.
   *
   * @param field the calendar field.
   * @return the highest minimum value for the given calendar field.
   * @see #getMinimum(int)
   * @see #getMaximum(int)
   * @see #getLeastMaximum(int)
   * @see #getActualMinimum(int)
   * @see #getActualMaximum(int)
   */
  @Override
  public int getGreatestMinimum(int field) {
    if (field == DAY_OF_MONTH) {
      BaseCalendar.Date d = getGregorianCutoverDate();
      long mon1 = getFixedDateMonth1(d, gregorianCutoverDate);
      d = getCalendarDate(mon1);
      return Math.max(MIN_VALUES[field], d.getDayOfMonth());
    }
    return MIN_VALUES[field];
  }

  /**
   * Returns the lowest maximum value for the given calendar field
   * of this <code>GregorianCalendar</code> instance. The lowest
   * maximum value is defined as the smallest value returned by
   * {@link #getActualMaximum(int)} for any possible time value,
   * taking into consideration the current values of the
   * {@link Calendar#getFirstDayOfWeek() getFirstDayOfWeek},
   * {@link Calendar#getMinimalDaysInFirstWeek() getMinimalDaysInFirstWeek},
   * {@link #getGregorianChange() getGregorianChange} and
   * {@link Calendar#getTimeZone() getTimeZone} methods.
   *
   * @param field the calendar field
   * @return the lowest maximum value for the given calendar field.
   * @see #getMinimum(int)
   * @see #getMaximum(int)
   * @see #getGreatestMinimum(int)
   * @see #getActualMinimum(int)
   * @see #getActualMaximum(int)
   */
  @Override
  public int getLeastMaximum(int field) {
    switch (field) {
      case MONTH:
      case DAY_OF_MONTH:
      case DAY_OF_YEAR:
      case WEEK_OF_YEAR:
      case WEEK_OF_MONTH:
      case DAY_OF_WEEK_IN_MONTH:
      case YEAR: {
        GregorianCalendar gc = (GregorianCalendar) clone();
        gc.setLenient(true);
        gc.setTimeInMillis(gregorianCutover);
        int v1 = gc.getActualMaximum(field);
        gc.setTimeInMillis(gregorianCutover - 1);
        int v2 = gc.getActualMaximum(field);
        return Math.min(LEAST_MAX_VALUES[field], Math.min(v1, v2));
      }
    }
    return LEAST_MAX_VALUES[field];
  }

  /**
   * Returns the minimum value that this calendar field could have,
   * taking into consideration the given time value and the current
   * values of the
   * {@link Calendar#getFirstDayOfWeek() getFirstDayOfWeek},
   * {@link Calendar#getMinimalDaysInFirstWeek() getMinimalDaysInFirstWeek},
   * {@link #getGregorianChange() getGregorianChange} and
   * {@link Calendar#getTimeZone() getTimeZone} methods.
   *
   * <p>For example, if the Gregorian change date is January 10,
   * 1970 and the date of this <code>GregorianCalendar</code> is
   * January 20, 1970, the actual minimum value of the
   * <code>DAY_OF_MONTH</code> field is 10 because the previous date
   * of January 10, 1970 is December 27, 1996 (in the Julian
   * calendar). Therefore, December 28, 1969 to January 9, 1970
   * don't exist.
   *
   * @param field the calendar field
   * @return the minimum of the given field for the time value of this <code>GregorianCalendar</code>
   * @see #getMinimum(int)
   * @see #getMaximum(int)
   * @see #getGreatestMinimum(int)
   * @see #getLeastMaximum(int)
   * @see #getActualMaximum(int)
   * @since 1.2
   */
  @Override
  public int getActualMinimum(int field) {
    if (field == DAY_OF_MONTH) {
      GregorianCalendar gc = getNormalizedCalendar();
      int year = gc.cdate.getNormalizedYear();
      if (year == gregorianCutoverYear || year == gregorianCutoverYearJulian) {
        long month1 = getFixedDateMonth1(gc.cdate, gc.calsys.getFixedDate(gc.cdate));
        BaseCalendar.Date d = getCalendarDate(month1);
        return d.getDayOfMonth();
      }
    }
    return getMinimum(field);
  }

  /**
   * Returns the maximum value that this calendar field could have,
   * taking into consideration the given time value and the current
   * values of the
   * {@link Calendar#getFirstDayOfWeek() getFirstDayOfWeek},
   * {@link Calendar#getMinimalDaysInFirstWeek() getMinimalDaysInFirstWeek},
   * {@link #getGregorianChange() getGregorianChange} and
   * {@link Calendar#getTimeZone() getTimeZone} methods.
   * For example, if the date of this instance is February 1, 2004,
   * the actual maximum value of the <code>DAY_OF_MONTH</code> field
   * is 29 because 2004 is a leap year, and if the date of this
   * instance is February 1, 2005, it's 28.
   *
   * <p>This method calculates the maximum value of {@link
   * Calendar#WEEK_OF_YEAR WEEK_OF_YEAR} based on the {@link
   * Calendar#YEAR YEAR} (calendar year) value, not the <a
   * href="#week_year">week year</a>. Call {@link
   * #getWeeksInWeekYear()} to get the maximum value of {@code
   * WEEK_OF_YEAR} in the week year of this {@code GregorianCalendar}.
   *
   * @param field the calendar field
   * @return the maximum of the given field for the time value of this <code>GregorianCalendar</code>
   * @see #getMinimum(int)
   * @see #getMaximum(int)
   * @see #getGreatestMinimum(int)
   * @see #getLeastMaximum(int)
   * @see #getActualMinimum(int)
   * @since 1.2
   */
  @Override
  public int getActualMaximum(int field) {
    final int fieldsForFixedMax = ERA_MASK | DAY_OF_WEEK_MASK | HOUR_MASK | AM_PM_MASK |
        HOUR_OF_DAY_MASK | MINUTE_MASK | SECOND_MASK | MILLISECOND_MASK |
        ZONE_OFFSET_MASK | DST_OFFSET_MASK;
    if ((fieldsForFixedMax & (1 << field)) != 0) {
      return getMaximum(field);
    }

    GregorianCalendar gc = getNormalizedCalendar();
    BaseCalendar.Date date = gc.cdate;
    BaseCalendar cal = gc.calsys;
    int normalizedYear = date.getNormalizedYear();

    int value = -1;
    switch (field) {
      case MONTH: {
        if (!gc.isCutoverYear(normalizedYear)) {
          value = DECEMBER;
          break;
        }

        // January 1 of the next year may or may not exist.
        long nextJan1;
        do {
          nextJan1 = gcal.getFixedDate(++normalizedYear, BaseCalendar.JANUARY, 1, null);
        } while (nextJan1 < gregorianCutoverDate);
        BaseCalendar.Date d = (BaseCalendar.Date) date.clone();
        cal.getCalendarDateFromFixedDate(d, nextJan1 - 1);
        value = d.getMonth() - 1;
      }
      break;

      case DAY_OF_MONTH: {
        value = cal.getMonthLength(date);
        if (!gc.isCutoverYear(normalizedYear) || date.getDayOfMonth() == value) {
          break;
        }

        // Handle cutover year.
        long fd = gc.getCurrentFixedDate();
        if (fd >= gregorianCutoverDate) {
          break;
        }
        int monthLength = gc.actualMonthLength();
        long monthEnd = gc.getFixedDateMonth1(gc.cdate, fd) + monthLength - 1;
        // Convert the fixed date to its calendar date.
        BaseCalendar.Date d = gc.getCalendarDate(monthEnd);
        value = d.getDayOfMonth();
      }
      break;

      case DAY_OF_YEAR: {
        if (!gc.isCutoverYear(normalizedYear)) {
          value = cal.getYearLength(date);
          break;
        }

        // Handle cutover year.
        long jan1;
        if (gregorianCutoverYear == gregorianCutoverYearJulian) {
          BaseCalendar cocal = gc.getCutoverCalendarSystem();
          jan1 = cocal.getFixedDate(normalizedYear, 1, 1, null);
        } else if (normalizedYear == gregorianCutoverYearJulian) {
          jan1 = cal.getFixedDate(normalizedYear, 1, 1, null);
        } else {
          jan1 = gregorianCutoverDate;
        }
        // January 1 of the next year may or may not exist.
        long nextJan1 = gcal.getFixedDate(++normalizedYear, 1, 1, null);
        if (nextJan1 < gregorianCutoverDate) {
          nextJan1 = gregorianCutoverDate;
        }
        assert jan1 <= cal.getFixedDate(date.getNormalizedYear(), date.getMonth(),
            date.getDayOfMonth(), date);
        assert nextJan1 >= cal.getFixedDate(date.getNormalizedYear(), date.getMonth(),
            date.getDayOfMonth(), date);
        value = (int) (nextJan1 - jan1);
      }
      break;

      case WEEK_OF_YEAR: {
        if (!gc.isCutoverYear(normalizedYear)) {
          // Get the day of week of January 1 of the year
          CalendarDate d = cal.newCalendarDate(TimeZone.NO_TIMEZONE);
          d.setDate(date.getYear(), BaseCalendar.JANUARY, 1);
          int dayOfWeek = cal.getDayOfWeek(d);
          // Normalize the day of week with the firstDayOfWeek value
          dayOfWeek -= getFirstDayOfWeek();
          if (dayOfWeek < 0) {
            dayOfWeek += 7;
          }
          value = 52;
          int magic = dayOfWeek + getMinimalDaysInFirstWeek() - 1;
          if ((magic == 6) ||
              (date.isLeapYear() && (magic == 5 || magic == 12))) {
            value++;
          }
          break;
        }

        if (gc == this) {
          gc = (GregorianCalendar) gc.clone();
        }
        int maxDayOfYear = getActualMaximum(DAY_OF_YEAR);
        gc.set(DAY_OF_YEAR, maxDayOfYear);
        value = gc.get(WEEK_OF_YEAR);
        if (internalGet(YEAR) != gc.getWeekYear()) {
          gc.set(DAY_OF_YEAR, maxDayOfYear - 7);
          value = gc.get(WEEK_OF_YEAR);
        }
      }
      break;

      case WEEK_OF_MONTH: {
        if (!gc.isCutoverYear(normalizedYear)) {
          CalendarDate d = cal.newCalendarDate(null);
          d.setDate(date.getYear(), date.getMonth(), 1);
          int dayOfWeek = cal.getDayOfWeek(d);
          int monthLength = cal.getMonthLength(d);
          dayOfWeek -= getFirstDayOfWeek();
          if (dayOfWeek < 0) {
            dayOfWeek += 7;
          }
          int nDaysFirstWeek = 7 - dayOfWeek; // # of days in the first week
          value = 3;
          if (nDaysFirstWeek >= getMinimalDaysInFirstWeek()) {
            value++;
          }
          monthLength -= nDaysFirstWeek + 7 * 3;
          if (monthLength > 0) {
            value++;
            if (monthLength > 7) {
              value++;
            }
          }
          break;
        }

        // Cutover year handling
        if (gc == this) {
          gc = (GregorianCalendar) gc.clone();
        }
        int y = gc.internalGet(YEAR);
        int m = gc.internalGet(MONTH);
        do {
          value = gc.get(WEEK_OF_MONTH);
          gc.add(WEEK_OF_MONTH, +1);
        } while (gc.get(YEAR) == y && gc.get(MONTH) == m);
      }
      break;

      case DAY_OF_WEEK_IN_MONTH: {
        // may be in the Gregorian cutover month
        int ndays, dow1;
        int dow = date.getDayOfWeek();
        if (!gc.isCutoverYear(normalizedYear)) {
          BaseCalendar.Date d = (BaseCalendar.Date) date.clone();
          ndays = cal.getMonthLength(d);
          d.setDayOfMonth(1);
          cal.normalize(d);
          dow1 = d.getDayOfWeek();
        } else {
          // Let a cloned GregorianCalendar take care of the cutover cases.
          if (gc == this) {
            gc = (GregorianCalendar) clone();
          }
          ndays = gc.actualMonthLength();
          gc.set(DAY_OF_MONTH, gc.getActualMinimum(DAY_OF_MONTH));
          dow1 = gc.get(DAY_OF_WEEK);
        }
        int x = dow - dow1;
        if (x < 0) {
          x += 7;
        }
        ndays -= x;
        value = (ndays + 6) / 7;
      }
      break;

      case YEAR:
            /* The year computation is no different, in principle, from the
             * others, however, the range of possible maxima is large.  In
             * addition, the way we know we've exceeded the range is different.
             * For these reasons, we use the special case code below to handle
             * this field.
             *
             * The actual maxima for YEAR depend on the type of calendar:
             *
             *     Gregorian = May 17, 292275056 BCE - Aug 17, 292278994 CE
             *     Julian    = Dec  2, 292269055 BCE - Jan  3, 292272993 CE
             *     Hybrid    = Dec  2, 292269055 BCE - Aug 17, 292278994 CE
             *
             * We know we've exceeded the maximum when either the month, date,
             * time, or era changes in response to setting the year.  We don't
             * check for month, date, and time here because the year and era are
             * sufficient to detect an invalid year setting.  NOTE: If code is
             * added to check the month and date in the future for some reason,
             * Feb 29 must be allowed to shift to Mar 1 when setting the year.
             */
      {
        if (gc == this) {
          gc = (GregorianCalendar) clone();
        }

        // Calculate the millisecond offset from the beginning
        // of the year of this calendar and adjust the max
        // year value if we are beyond the limit in the max
        // year.
        long current = gc.getYearOffsetInMillis();

        if (gc.internalGetEra() == CE) {
          gc.setTimeInMillis(Long.MAX_VALUE);
          value = gc.get(YEAR);
          long maxEnd = gc.getYearOffsetInMillis();
          if (current > maxEnd) {
            value--;
          }
        } else {
          CalendarSystem mincal = gc.getTimeInMillis() >= gregorianCutover ?
              gcal : getJulianCalendarSystem();
          CalendarDate d = mincal.getCalendarDate(Long.MIN_VALUE, getZone());
          long maxEnd = (cal.getDayOfYear(d) - 1) * 24 + d.getHours();
          maxEnd *= 60;
          maxEnd += d.getMinutes();
          maxEnd *= 60;
          maxEnd += d.getSeconds();
          maxEnd *= 1000;
          maxEnd += d.getMillis();
          value = d.getYear();
          if (value <= 0) {
            assert mincal == gcal;
            value = 1 - value;
          }
          if (current < maxEnd) {
            value--;
          }
        }
      }
      break;

      default:
        throw new ArrayIndexOutOfBoundsException(field);
    }
    return value;
  }

  /**
   * Returns the millisecond offset from the beginning of this
   * year. This Calendar object must have been normalized.
   */
  private long getYearOffsetInMillis() {
    long t = (internalGet(DAY_OF_YEAR) - 1) * 24;
    t += internalGet(HOUR_OF_DAY);
    t *= 60;
    t += internalGet(MINUTE);
    t *= 60;
    t += internalGet(SECOND);
    t *= 1000;
    return t + internalGet(MILLISECOND) -
        (internalGet(ZONE_OFFSET) + internalGet(DST_OFFSET));
  }

  @Override
  public Object clone() {
    GregorianCalendar other = (GregorianCalendar) super.clone();

    other.gdate = (BaseCalendar.Date) gdate.clone();
    if (cdate != null) {
      if (cdate != gdate) {
        other.cdate = (BaseCalendar.Date) cdate.clone();
      } else {
        other.cdate = other.gdate;
      }
    }
    other.originalFields = null;
    other.zoneOffsets = null;
    return other;
  }

  @Override
  public TimeZone getTimeZone() {
    TimeZone zone = super.getTimeZone();
    // To share the zone by CalendarDates
    gdate.setZone(zone);
    if (cdate != null && cdate != gdate) {
      cdate.setZone(zone);
    }
    return zone;
  }

  @Override
  public void setTimeZone(TimeZone zone) {
    super.setTimeZone(zone);
    // To share the zone by CalendarDates
    gdate.setZone(zone);
    if (cdate != null && cdate != gdate) {
      cdate.setZone(zone);
    }
  }

  /**
   * Returns {@code true} indicating this {@code GregorianCalendar}
   * supports week dates.
   *
   * @return {@code true} (always)
   * @see #getWeekYear()
   * @see #setWeekDate(int, int, int)
   * @see #getWeeksInWeekYear()
   * @since 1.7
   */
  @Override
  public final boolean isWeekDateSupported() {
    return true;
  }

  /**
   * Returns the <a href="#week_year">week year</a> represented by this
   * {@code GregorianCalendar}. The dates in the weeks between 1 and the
   * maximum week number of the week year have the same week year value
   * that may be one year before or after the {@link Calendar#YEAR YEAR}
   * (calendar year) value.
   *
   * <p>This method calls {@link Calendar#complete()} before
   * calculating the week year.
   *
   * @return the week year represented by this {@code GregorianCalendar}. If the {@link Calendar#ERA
   * ERA} value is {@link #BC}, the year is represented by 0 or a negative number: BC 1 is 0, BC 2
   * is -1, BC 3 is -2, and so on.
   * @throws IllegalArgumentException if any of the calendar fields is invalid in non-lenient mode.
   * @see #isWeekDateSupported()
   * @see #getWeeksInWeekYear()
   * @see Calendar#getFirstDayOfWeek()
   * @see Calendar#getMinimalDaysInFirstWeek()
   * @since 1.7
   */
  @Override
  public int getWeekYear() {
    int year = get(YEAR); // implicitly calls complete()
    if (internalGetEra() == BCE) {
      year = 1 - year;
    }

    // Fast path for the Gregorian calendar years that are never
    // affected by the Julian-Gregorian transition
    if (year > gregorianCutoverYear + 1) {
      int weekOfYear = internalGet(WEEK_OF_YEAR);
      if (internalGet(MONTH) == JANUARY) {
        if (weekOfYear >= 52) {
          --year;
        }
      } else {
        if (weekOfYear == 1) {
          ++year;
        }
      }
      return year;
    }

    // General (slow) path
    int dayOfYear = internalGet(DAY_OF_YEAR);
    int maxDayOfYear = getActualMaximum(DAY_OF_YEAR);
    int minimalDays = getMinimalDaysInFirstWeek();

    // Quickly check the possibility of year adjustments before
    // cloning this GregorianCalendar.
    if (dayOfYear > minimalDays && dayOfYear < (maxDayOfYear - 6)) {
      return year;
    }

    // Create a clone to work on the calculation
    GregorianCalendar cal = (GregorianCalendar) clone();
    cal.setLenient(true);
    // Use GMT so that intermediate date calculations won't
    // affect the time of day fields.
    cal.setTimeZone(TimeZone.getTimeZone("GMT"));
    // Go to the first day of the year, which is usually January 1.
    cal.set(DAY_OF_YEAR, 1);
    cal.complete();

    // Get the first day of the first day-of-week in the year.
    int delta = getFirstDayOfWeek() - cal.get(DAY_OF_WEEK);
    if (delta != 0) {
      if (delta < 0) {
        delta += 7;
      }
      cal.add(DAY_OF_YEAR, delta);
    }
    int minDayOfYear = cal.get(DAY_OF_YEAR);
    if (dayOfYear < minDayOfYear) {
      if (minDayOfYear <= minimalDays) {
        --year;
      }
    } else {
      cal.set(YEAR, year + 1);
      cal.set(DAY_OF_YEAR, 1);
      cal.complete();
      int del = getFirstDayOfWeek() - cal.get(DAY_OF_WEEK);
      if (del != 0) {
        if (del < 0) {
          del += 7;
        }
        cal.add(DAY_OF_YEAR, del);
      }
      minDayOfYear = cal.get(DAY_OF_YEAR) - 1;
      if (minDayOfYear == 0) {
        minDayOfYear = 7;
      }
      if (minDayOfYear >= minimalDays) {
        int days = maxDayOfYear - dayOfYear + 1;
        if (days <= (7 - minDayOfYear)) {
          ++year;
        }
      }
    }
    return year;
  }

  /**
   * Sets this {@code GregorianCalendar} to the date given by the
   * date specifiers - <a href="#week_year">{@code weekYear}</a>,
   * {@code weekOfYear}, and {@code dayOfWeek}. {@code weekOfYear}
   * follows the <a href="#week_and_year">{@code WEEK_OF_YEAR}
   * numbering</a>.  The {@code dayOfWeek} value must be one of the
   * {@link Calendar#DAY_OF_WEEK DAY_OF_WEEK} values: {@link
   * Calendar#SUNDAY SUNDAY} to {@link Calendar#SATURDAY SATURDAY}.
   *
   * <p>Note that the numeric day-of-week representation differs from
   * the ISO 8601 standard, and that the {@code weekOfYear}
   * numbering is compatible with the standard when {@code
   * getFirstDayOfWeek()} is {@code MONDAY} and {@code
   * getMinimalDaysInFirstWeek()} is 4.
   *
   * <p>Unlike the {@code set} method, all of the calendar fields
   * and the instant of time value are calculated upon return.
   *
   * <p>If {@code weekOfYear} is out of the valid week-of-year
   * range in {@code weekYear}, the {@code weekYear}
   * and {@code weekOfYear} values are adjusted in lenient
   * mode, or an {@code IllegalArgumentException} is thrown in
   * non-lenient mode.
   *
   * @param weekYear the week year
   * @param weekOfYear the week number based on {@code weekYear}
   * @param dayOfWeek the day of week value: one of the constants for the {@link #DAY_OF_WEEK
   * DAY_OF_WEEK} field: {@link Calendar#SUNDAY SUNDAY}, ..., {@link Calendar#SATURDAY SATURDAY}.
   * @throws IllegalArgumentException if any of the given date specifiers is invalid, or if any of
   * the calendar fields are inconsistent with the given date specifiers in non-lenient mode
   * @see GregorianCalendar#isWeekDateSupported()
   * @see Calendar#getFirstDayOfWeek()
   * @see Calendar#getMinimalDaysInFirstWeek()
   * @since 1.7
   */
  @Override
  public void setWeekDate(int weekYear, int weekOfYear, int dayOfWeek) {
    if (dayOfWeek < SUNDAY || dayOfWeek > SATURDAY) {
      throw new IllegalArgumentException("invalid dayOfWeek: " + dayOfWeek);
    }

    // To avoid changing the time of day fields by date
    // calculations, use a clone with the GMT time zone.
    GregorianCalendar gc = (GregorianCalendar) clone();
    gc.setLenient(true);
    int era = gc.get(ERA);
    gc.clear();
    gc.setTimeZone(TimeZone.getTimeZone("GMT"));
    gc.set(ERA, era);
    gc.set(YEAR, weekYear);
    gc.set(WEEK_OF_YEAR, 1);
    gc.set(DAY_OF_WEEK, getFirstDayOfWeek());
    int days = dayOfWeek - getFirstDayOfWeek();
    if (days < 0) {
      days += 7;
    }
    days += 7 * (weekOfYear - 1);
    if (days != 0) {
      gc.add(DAY_OF_YEAR, days);
    } else {
      gc.complete();
    }

    if (!isLenient() &&
        (gc.getWeekYear() != weekYear
            || gc.internalGet(WEEK_OF_YEAR) != weekOfYear
            || gc.internalGet(DAY_OF_WEEK) != dayOfWeek)) {
      throw new IllegalArgumentException();
    }

    set(ERA, gc.internalGet(ERA));
    set(YEAR, gc.internalGet(YEAR));
    set(MONTH, gc.internalGet(MONTH));
    set(DAY_OF_MONTH, gc.internalGet(DAY_OF_MONTH));

    // to avoid throwing an IllegalArgumentException in
    // non-lenient, set WEEK_OF_YEAR internally
    internalSet(WEEK_OF_YEAR, weekOfYear);
    complete();
  }

  /**
   * Returns the number of weeks in the <a href="#week_year">week year</a>
   * represented by this {@code GregorianCalendar}.
   *
   * <p>For example, if this {@code GregorianCalendar}'s date is
   * December 31, 2008 with <a href="#iso8601_compatible_setting">the ISO
   * 8601 compatible setting</a>, this method will return 53 for the
   * period: December 29, 2008 to January 3, 2010 while {@link
   * #getActualMaximum(int) getActualMaximum(WEEK_OF_YEAR)} will return
   * 52 for the period: December 31, 2007 to December 28, 2008.
   *
   * @return the number of weeks in the week year.
   * @see Calendar#WEEK_OF_YEAR
   * @see #getWeekYear()
   * @see #getActualMaximum(int)
   * @since 1.7
   */
  @Override
  public int getWeeksInWeekYear() {
    GregorianCalendar gc = getNormalizedCalendar();
    int weekYear = gc.getWeekYear();
    if (weekYear == gc.internalGet(YEAR)) {
      return gc.getActualMaximum(WEEK_OF_YEAR);
    }

    // Use the 2nd week for calculating the max of WEEK_OF_YEAR
    if (gc == this) {
      gc = (GregorianCalendar) gc.clone();
    }
    gc.setWeekDate(weekYear, 2, internalGet(DAY_OF_WEEK));
    return gc.getActualMaximum(WEEK_OF_YEAR);
  }

/////////////////////////////
// Time => Fields computation
/////////////////////////////

  /**
   * The fixed date corresponding to gdate. If the value is
   * Long.MIN_VALUE, the fixed date value is unknown. Currently,
   * Julian calendar dates are not cached.
   */
  transient private long cachedFixedDate = Long.MIN_VALUE;

  /**
   * Converts the time value (millisecond offset from the <a
   * href="Calendar.html#Epoch">Epoch</a>) to calendar field values.
   * The time is <em>not</em>
   * recomputed first; to recompute the time, then the fields, call the
   * <code>complete</code> method.
   *
   * @see Calendar#complete
   */
  @Override
  protected void computeFields() {
    int mask;
    if (isPartiallyNormalized()) {
      // Determine which calendar fields need to be computed.
      mask = getSetStateFields();
      int fieldMask = ~mask & ALL_FIELDS;
      // We have to call computTime in case calsys == null in
      // order to set calsys and cdate. (6263644)
      if (fieldMask != 0 || calsys == null) {
        mask |= computeFields(fieldMask,
            mask & (ZONE_OFFSET_MASK | DST_OFFSET_MASK));
        assert mask == ALL_FIELDS;
      }
    } else {
      mask = ALL_FIELDS;
      computeFields(mask, 0);
    }
    // After computing all the fields, set the field state to `COMPUTED'.
    setFieldsComputed(mask);
  }

  /**
   * This computeFields implements the conversion from UTC
   * (millisecond offset from the Epoch) to calendar
   * field values. fieldMask specifies which fields to change the
   * setting state to COMPUTED, although all fields are set to
   * the correct values. This is required to fix 4685354.
   *
   * @param fieldMask a bit mask to specify which fields to change the setting state.
   * @param tzMask a bit mask to specify which time zone offset fields to be used for time
   * calculations
   * @return a new field mask that indicates what field values have actually been set.
   */
  private int computeFields(int fieldMask, int tzMask) {
    int zoneOffset = 0;
    TimeZone tz = getZone();
    if (zoneOffsets == null) {
      zoneOffsets = new int[2];
    }
    if (tzMask != (ZONE_OFFSET_MASK | DST_OFFSET_MASK)) {
      if (tz instanceof ZoneInfo) {
        zoneOffset = ((ZoneInfo) tz).getOffsets(time, zoneOffsets);
      } else {
        zoneOffset = tz.getOffset(time);
        zoneOffsets[0] = tz.getRawOffset();
        zoneOffsets[1] = zoneOffset - zoneOffsets[0];
      }
    }
    if (tzMask != 0) {
      if (isFieldSet(tzMask, ZONE_OFFSET)) {
        zoneOffsets[0] = internalGet(ZONE_OFFSET);
      }
      if (isFieldSet(tzMask, DST_OFFSET)) {
        zoneOffsets[1] = internalGet(DST_OFFSET);
      }
      zoneOffset = zoneOffsets[0] + zoneOffsets[1];
    }

    // By computing time and zoneOffset separately, we can take
    // the wider range of time+zoneOffset than the previous
    // implementation.
    long fixedDate = zoneOffset / ONE_DAY;
    int timeOfDay = zoneOffset % (int) ONE_DAY;
    fixedDate += time / ONE_DAY;
    timeOfDay += (int) (time % ONE_DAY);
    if (timeOfDay >= ONE_DAY) {
      timeOfDay -= ONE_DAY;
      ++fixedDate;
    } else {
      while (timeOfDay < 0) {
        timeOfDay += ONE_DAY;
        --fixedDate;
      }
    }
    fixedDate += EPOCH_OFFSET;

    int era = CE;
    int year;
    if (fixedDate >= gregorianCutoverDate) {
      // Handle Gregorian dates.
      assert cachedFixedDate == Long.MIN_VALUE || gdate.isNormalized()
          : "cache control: not normalized";
      assert cachedFixedDate == Long.MIN_VALUE ||
          gcal.getFixedDate(gdate.getNormalizedYear(),
              gdate.getMonth(),
              gdate.getDayOfMonth(), gdate)
              == cachedFixedDate
          : "cache control: inconsictency" +
          ", cachedFixedDate=" + cachedFixedDate +
          ", computed=" +
          gcal.getFixedDate(gdate.getNormalizedYear(),
              gdate.getMonth(),
              gdate.getDayOfMonth(),
              gdate) +
          ", date=" + gdate;

      // See if we can use gdate to avoid date calculation.
      if (fixedDate != cachedFixedDate) {
        gcal.getCalendarDateFromFixedDate(gdate, fixedDate);
        cachedFixedDate = fixedDate;
      }

      year = gdate.getYear();
      if (year <= 0) {
        year = 1 - year;
        era = BCE;
      }
      calsys = gcal;
      cdate = gdate;
      assert cdate.getDayOfWeek() > 0 : "dow=" + cdate.getDayOfWeek() + ", date=" + cdate;
    } else {
      // Handle Julian calendar dates.
      calsys = getJulianCalendarSystem();
      cdate = (BaseCalendar.Date) jcal.newCalendarDate(getZone());
      jcal.getCalendarDateFromFixedDate(cdate, fixedDate);
      Era e = cdate.getEra();
      if (e == jeras[0]) {
        era = BCE;
      }
      year = cdate.getYear();
    }

    // Always set the ERA and YEAR values.
    internalSet(ERA, era);
    internalSet(YEAR, year);
    int mask = fieldMask | (ERA_MASK | YEAR_MASK);

    int month = cdate.getMonth() - 1; // 0-based
    int dayOfMonth = cdate.getDayOfMonth();

    // Set the basic date fields.
    if ((fieldMask & (MONTH_MASK | DAY_OF_MONTH_MASK | DAY_OF_WEEK_MASK))
        != 0) {
      internalSet(MONTH, month);
      internalSet(DAY_OF_MONTH, dayOfMonth);
      internalSet(DAY_OF_WEEK, cdate.getDayOfWeek());
      mask |= MONTH_MASK | DAY_OF_MONTH_MASK | DAY_OF_WEEK_MASK;
    }

    if ((fieldMask & (HOUR_OF_DAY_MASK | AM_PM_MASK | HOUR_MASK
        | MINUTE_MASK | SECOND_MASK | MILLISECOND_MASK)) != 0) {
      if (timeOfDay != 0) {
        int hours = timeOfDay / ONE_HOUR;
        internalSet(HOUR_OF_DAY, hours);
        internalSet(AM_PM, hours / 12); // Assume AM == 0
        internalSet(HOUR, hours % 12);
        int r = timeOfDay % ONE_HOUR;
        internalSet(MINUTE, r / ONE_MINUTE);
        r %= ONE_MINUTE;
        internalSet(SECOND, r / ONE_SECOND);
        internalSet(MILLISECOND, r % ONE_SECOND);
      } else {
        internalSet(HOUR_OF_DAY, 0);
        internalSet(AM_PM, AM);
        internalSet(HOUR, 0);
        internalSet(MINUTE, 0);
        internalSet(SECOND, 0);
        internalSet(MILLISECOND, 0);
      }
      mask |= (HOUR_OF_DAY_MASK | AM_PM_MASK | HOUR_MASK
          | MINUTE_MASK | SECOND_MASK | MILLISECOND_MASK);
    }

    if ((fieldMask & (ZONE_OFFSET_MASK | DST_OFFSET_MASK)) != 0) {
      internalSet(ZONE_OFFSET, zoneOffsets[0]);
      internalSet(DST_OFFSET, zoneOffsets[1]);
      mask |= (ZONE_OFFSET_MASK | DST_OFFSET_MASK);
    }

    if ((fieldMask & (DAY_OF_YEAR_MASK | WEEK_OF_YEAR_MASK | WEEK_OF_MONTH_MASK
        | DAY_OF_WEEK_IN_MONTH_MASK)) != 0) {
      int normalizedYear = cdate.getNormalizedYear();
      long fixedDateJan1 = calsys.getFixedDate(normalizedYear, 1, 1, cdate);
      int dayOfYear = (int) (fixedDate - fixedDateJan1) + 1;
      long fixedDateMonth1 = fixedDate - dayOfMonth + 1;
      int cutoverGap = 0;
      int cutoverYear = (calsys == gcal) ? gregorianCutoverYear : gregorianCutoverYearJulian;
      int relativeDayOfMonth = dayOfMonth - 1;

      // If we are in the cutover year, we need some special handling.
      if (normalizedYear == cutoverYear) {
        // Need to take care of the "missing" days.
        if (gregorianCutoverYearJulian <= gregorianCutoverYear) {
          // We need to find out where we are. The cutover
          // gap could even be more than one year.  (One
          // year difference in ~48667 years.)
          fixedDateJan1 = getFixedDateJan1(cdate, fixedDate);
          if (fixedDate >= gregorianCutoverDate) {
            fixedDateMonth1 = getFixedDateMonth1(cdate, fixedDate);
          }
        }
        int realDayOfYear = (int) (fixedDate - fixedDateJan1) + 1;
        cutoverGap = dayOfYear - realDayOfYear;
        dayOfYear = realDayOfYear;
        relativeDayOfMonth = (int) (fixedDate - fixedDateMonth1);
      }
      internalSet(DAY_OF_YEAR, dayOfYear);
      internalSet(DAY_OF_WEEK_IN_MONTH, relativeDayOfMonth / 7 + 1);

      int weekOfYear = getWeekNumber(fixedDateJan1, fixedDate);

      // The spec is to calculate WEEK_OF_YEAR in the
      // ISO8601-style. This creates problems, though.
      if (weekOfYear == 0) {
        // If the date belongs to the last week of the
        // previous year, use the week number of "12/31" of
        // the "previous" year. Again, if the previous year is
        // the Gregorian cutover year, we need to take care of
        // it.  Usually the previous day of January 1 is
        // December 31, which is not always true in
        // GregorianCalendar.
        long fixedDec31 = fixedDateJan1 - 1;
        long prevJan1 = fixedDateJan1 - 365;
        if (normalizedYear > (cutoverYear + 1)) {
          if (CalendarUtils.isGregorianLeapYear(normalizedYear - 1)) {
            --prevJan1;
          }
        } else if (normalizedYear <= gregorianCutoverYearJulian) {
          if (CalendarUtils.isJulianLeapYear(normalizedYear - 1)) {
            --prevJan1;
          }
        } else {
          BaseCalendar calForJan1 = calsys;
          //int prevYear = normalizedYear - 1;
          int prevYear = getCalendarDate(fixedDec31).getNormalizedYear();
          if (prevYear == gregorianCutoverYear) {
            calForJan1 = getCutoverCalendarSystem();
            if (calForJan1 == jcal) {
              prevJan1 = calForJan1.getFixedDate(prevYear,
                  BaseCalendar.JANUARY,
                  1,
                  null);
            } else {
              prevJan1 = gregorianCutoverDate;
              calForJan1 = gcal;
            }
          } else if (prevYear <= gregorianCutoverYearJulian) {
            calForJan1 = getJulianCalendarSystem();
            prevJan1 = calForJan1.getFixedDate(prevYear,
                BaseCalendar.JANUARY,
                1,
                null);
          }
        }
        weekOfYear = getWeekNumber(prevJan1, fixedDec31);
      } else {
        if (normalizedYear > gregorianCutoverYear ||
            normalizedYear < (gregorianCutoverYearJulian - 1)) {
          // Regular years
          if (weekOfYear >= 52) {
            long nextJan1 = fixedDateJan1 + 365;
            if (cdate.isLeapYear()) {
              nextJan1++;
            }
            long nextJan1st = BaseCalendar.getDayOfWeekDateOnOrBefore(nextJan1 + 6,
                getFirstDayOfWeek());
            int ndays = (int) (nextJan1st - nextJan1);
            if (ndays >= getMinimalDaysInFirstWeek() && fixedDate >= (nextJan1st - 7)) {
              // The first days forms a week in which the date is included.
              weekOfYear = 1;
            }
          }
        } else {
          BaseCalendar calForJan1 = calsys;
          int nextYear = normalizedYear + 1;
          if (nextYear == (gregorianCutoverYearJulian + 1) &&
              nextYear < gregorianCutoverYear) {
            // In case the gap is more than one year.
            nextYear = gregorianCutoverYear;
          }
          if (nextYear == gregorianCutoverYear) {
            calForJan1 = getCutoverCalendarSystem();
          }

          long nextJan1;
          if (nextYear > gregorianCutoverYear
              || gregorianCutoverYearJulian == gregorianCutoverYear
              || nextYear == gregorianCutoverYearJulian) {
            nextJan1 = calForJan1.getFixedDate(nextYear,
                BaseCalendar.JANUARY,
                1,
                null);
          } else {
            nextJan1 = gregorianCutoverDate;
            calForJan1 = gcal;
          }

          long nextJan1st = BaseCalendar.getDayOfWeekDateOnOrBefore(nextJan1 + 6,
              getFirstDayOfWeek());
          int ndays = (int) (nextJan1st - nextJan1);
          if (ndays >= getMinimalDaysInFirstWeek() && fixedDate >= (nextJan1st - 7)) {
            // The first days forms a week in which the date is included.
            weekOfYear = 1;
          }
        }
      }
      internalSet(WEEK_OF_YEAR, weekOfYear);
      internalSet(WEEK_OF_MONTH, getWeekNumber(fixedDateMonth1, fixedDate));
      mask |= (DAY_OF_YEAR_MASK | WEEK_OF_YEAR_MASK | WEEK_OF_MONTH_MASK
          | DAY_OF_WEEK_IN_MONTH_MASK);
    }
    return mask;
  }

  /**
   * Returns the number of weeks in a period between fixedDay1 and
   * fixedDate. The getFirstDayOfWeek-getMinimalDaysInFirstWeek rule
   * is applied to calculate the number of weeks.
   *
   * @param fixedDay1 the fixed date of the first day of the period
   * @param fixedDate the fixed date of the last day of the period
   * @return the number of weeks of the given period
   */
  private int getWeekNumber(long fixedDay1, long fixedDate) {
    // We can always use `gcal' since Julian and Gregorian are the
    // same thing for this calculation.
    long fixedDay1st = Gregorian.getDayOfWeekDateOnOrBefore(fixedDay1 + 6,
        getFirstDayOfWeek());
    int ndays = (int) (fixedDay1st - fixedDay1);
    assert ndays <= 7;
    if (ndays >= getMinimalDaysInFirstWeek()) {
      fixedDay1st -= 7;
    }
    int normalizedDayOfPeriod = (int) (fixedDate - fixedDay1st);
    if (normalizedDayOfPeriod >= 0) {
      return normalizedDayOfPeriod / 7 + 1;
    }
    return CalendarUtils.floorDivide(normalizedDayOfPeriod, 7) + 1;
  }

  /**
   * Converts calendar field values to the time value (millisecond
   * offset from the <a href="Calendar.html#Epoch">Epoch</a>).
   *
   * @throws IllegalArgumentException if any calendar fields are invalid.
   */
  @Override
  protected void computeTime() {
    // In non-lenient mode, perform brief checking of calendar
    // fields which have been set externally. Through this
    // checking, the field values are stored in originalFields[]
    // to see if any of them are normalized later.
    if (!isLenient()) {
      if (originalFields == null) {
        originalFields = new int[FIELD_COUNT];
      }
      for (int field = 0; field < FIELD_COUNT; field++) {
        int value = internalGet(field);
        if (isExternallySet(field)) {
          // Quick validation for any out of range values
          if (value < getMinimum(field) || value > getMaximum(field)) {
            throw new IllegalArgumentException(getFieldName(field));
          }
        }
        originalFields[field] = value;
      }
    }

    // Let the super class determine which calendar fields to be
    // used to calculate the time.
    int fieldMask = selectFields();

    // The year defaults to the epoch start. We don't check
    // fieldMask for YEAR because YEAR is a mandatory field to
    // determine the date.
    int year = isSet(YEAR) ? internalGet(YEAR) : EPOCH_YEAR;

    int era = internalGetEra();
    if (era == BCE) {
      year = 1 - year;
    } else if (era != CE) {
      // Even in lenient mode we disallow ERA values other than CE & BCE.
      // (The same normalization rule as add()/roll() could be
      // applied here in lenient mode. But this checking is kept
      // unchanged for compatibility as of 1.5.)
      throw new IllegalArgumentException("Invalid era");
    }

    // If year is 0 or negative, we need to set the ERA value later.
    if (year <= 0 && !isSet(ERA)) {
      fieldMask |= ERA_MASK;
      setFieldsComputed(ERA_MASK);
    }

    // Calculate the time of day. We rely on the convention that
    // an UNSET field has 0.
    long timeOfDay = 0;
    if (isFieldSet(fieldMask, HOUR_OF_DAY)) {
      timeOfDay += (long) internalGet(HOUR_OF_DAY);
    } else {
      timeOfDay += internalGet(HOUR);
      // The default value of AM_PM is 0 which designates AM.
      if (isFieldSet(fieldMask, AM_PM)) {
        timeOfDay += 12 * internalGet(AM_PM);
      }
    }
    timeOfDay *= 60;
    timeOfDay += internalGet(MINUTE);
    timeOfDay *= 60;
    timeOfDay += internalGet(SECOND);
    timeOfDay *= 1000;
    timeOfDay += internalGet(MILLISECOND);

    // Convert the time of day to the number of days and the
    // millisecond offset from midnight.
    long fixedDate = timeOfDay / ONE_DAY;
    timeOfDay %= ONE_DAY;
    while (timeOfDay < 0) {
      timeOfDay += ONE_DAY;
      --fixedDate;
    }

    // Calculate the fixed date since January 1, 1 (Gregorian).
    calculateFixedDate:
    {
      long gfd, jfd;
      if (year > gregorianCutoverYear && year > gregorianCutoverYearJulian) {
        gfd = fixedDate + getFixedDate(gcal, year, fieldMask);
        if (gfd >= gregorianCutoverDate) {
          fixedDate = gfd;
          break calculateFixedDate;
        }
        jfd = fixedDate + getFixedDate(getJulianCalendarSystem(), year, fieldMask);
      } else if (year < gregorianCutoverYear && year < gregorianCutoverYearJulian) {
        jfd = fixedDate + getFixedDate(getJulianCalendarSystem(), year, fieldMask);
        if (jfd < gregorianCutoverDate) {
          fixedDate = jfd;
          break calculateFixedDate;
        }
        gfd = jfd;
      } else {
        jfd = fixedDate + getFixedDate(getJulianCalendarSystem(), year, fieldMask);
        gfd = fixedDate + getFixedDate(gcal, year, fieldMask);
      }

      // Now we have to determine which calendar date it is.

      // If the date is relative from the beginning of the year
      // in the Julian calendar, then use jfd;
      if (isFieldSet(fieldMask, DAY_OF_YEAR) || isFieldSet(fieldMask, WEEK_OF_YEAR)) {
        if (gregorianCutoverYear == gregorianCutoverYearJulian) {
          fixedDate = jfd;
          break calculateFixedDate;
        } else if (year == gregorianCutoverYear) {
          fixedDate = gfd;
          break calculateFixedDate;
        }
      }

      if (gfd >= gregorianCutoverDate) {
        if (jfd >= gregorianCutoverDate) {
          fixedDate = gfd;
        } else {
          // The date is in an "overlapping" period. No way
          // to disambiguate it. Determine it using the
          // previous date calculation.
          if (calsys == gcal || calsys == null) {
            fixedDate = gfd;
          } else {
            fixedDate = jfd;
          }
        }
      } else {
        if (jfd < gregorianCutoverDate) {
          fixedDate = jfd;
        } else {
          // The date is in a "missing" period.
          if (!isLenient()) {
            throw new IllegalArgumentException("the specified date doesn't exist");
          }
          // Take the Julian date for compatibility, which
          // will produce a Gregorian date.
          fixedDate = jfd;
        }
      }
    }

    // millis represents local wall-clock time in milliseconds.
    long millis = (fixedDate - EPOCH_OFFSET) * ONE_DAY + timeOfDay;

    // Compute the time zone offset and DST offset.  There are two potential
    // ambiguities here.  We'll assume a 2:00 am (wall time) switchover time
    // for discussion purposes here.
    // 1. The transition into DST.  Here, a designated time of 2:00 am - 2:59 am
    //    can be in standard or in DST depending.  However, 2:00 am is an invalid
    //    representation (the representation jumps from 1:59:59 am Std to 3:00:00 am DST).
    //    We assume standard time.
    // 2. The transition out of DST.  Here, a designated time of 1:00 am - 1:59 am
    //    can be in standard or DST.  Both are valid representations (the rep
    //    jumps from 1:59:59 DST to 1:00:00 Std).
    //    Again, we assume standard time.
    // We use the TimeZone object, unless the user has explicitly set the ZONE_OFFSET
    // or DST_OFFSET fields; then we use those fields.
    TimeZone zone = getZone();
    if (zoneOffsets == null) {
      zoneOffsets = new int[2];
    }
    int tzMask = fieldMask & (ZONE_OFFSET_MASK | DST_OFFSET_MASK);
    if (tzMask != (ZONE_OFFSET_MASK | DST_OFFSET_MASK)) {
      if (zone instanceof ZoneInfo) {
        ((ZoneInfo) zone).getOffsetsByWall(millis, zoneOffsets);
      } else {
        int gmtOffset = isFieldSet(fieldMask, ZONE_OFFSET) ?
            internalGet(ZONE_OFFSET) : zone.getRawOffset();
        zone.getOffsets(millis - gmtOffset, zoneOffsets);
      }
    }
    if (tzMask != 0) {
      if (isFieldSet(tzMask, ZONE_OFFSET)) {
        zoneOffsets[0] = internalGet(ZONE_OFFSET);
      }
      if (isFieldSet(tzMask, DST_OFFSET)) {
        zoneOffsets[1] = internalGet(DST_OFFSET);
      }
    }

    // Adjust the time zone offset values to get the UTC time.
    millis -= zoneOffsets[0] + zoneOffsets[1];

    // Set this calendar's time in milliseconds
    time = millis;

    int mask = computeFields(fieldMask | getSetStateFields(), tzMask);

    if (!isLenient()) {
      for (int field = 0; field < FIELD_COUNT; field++) {
        if (!isExternallySet(field)) {
          continue;
        }
        if (originalFields[field] != internalGet(field)) {
          String s = originalFields[field] + " -> " + internalGet(field);
          // Restore the original field values
          System.arraycopy(originalFields, 0, fields, 0, fields.length);
          throw new IllegalArgumentException(getFieldName(field) + ": " + s);
        }
      }
    }
    setFieldsNormalized(mask);
  }

  /**
   * Computes the fixed date under either the Gregorian or the
   * Julian calendar, using the given year and the specified calendar fields.
   *
   * @param cal the CalendarSystem to be used for the date calculation
   * @param year the normalized year number, with 0 indicating the year 1 BCE, -1 indicating 2 BCE,
   * etc.
   * @param fieldMask the calendar fields to be used for the date calculation
   * @return the fixed date
   * @see Calendar#selectFields
   */
  private long getFixedDate(BaseCalendar cal, int year, int fieldMask) {
    int month = JANUARY;
    if (isFieldSet(fieldMask, MONTH)) {
      // No need to check if MONTH has been set (no isSet(MONTH)
      // call) since its unset value happens to be JANUARY (0).
      month = internalGet(MONTH);

      // If the month is out of range, adjust it into range
      if (month > DECEMBER) {
        year += month / 12;
        month %= 12;
      } else if (month < JANUARY) {
        int[] rem = new int[1];
        year += CalendarUtils.floorDivide(month, 12, rem);
        month = rem[0];
      }
    }

    // Get the fixed date since Jan 1, 1 (Gregorian). We are on
    // the first day of either `month' or January in 'year'.
    long fixedDate = cal.getFixedDate(year, month + 1, 1,
        cal == gcal ? gdate : null);
    if (isFieldSet(fieldMask, MONTH)) {
      // Month-based calculations
      if (isFieldSet(fieldMask, DAY_OF_MONTH)) {
        // We are on the first day of the month. Just add the
        // offset if DAY_OF_MONTH is set. If the isSet call
        // returns false, that means DAY_OF_MONTH has been
        // selected just because of the selected
        // combination. We don't need to add any since the
        // default value is the 1st.
        if (isSet(DAY_OF_MONTH)) {
          // To avoid underflow with DAY_OF_MONTH-1, add
          // DAY_OF_MONTH, then subtract 1.
          fixedDate += internalGet(DAY_OF_MONTH);
          fixedDate--;
        }
      } else {
        if (isFieldSet(fieldMask, WEEK_OF_MONTH)) {
          long firstDayOfWeek = BaseCalendar.getDayOfWeekDateOnOrBefore(fixedDate + 6,
              getFirstDayOfWeek());
          // If we have enough days in the first week, then
          // move to the previous week.
          if ((firstDayOfWeek - fixedDate) >= getMinimalDaysInFirstWeek()) {
            firstDayOfWeek -= 7;
          }
          if (isFieldSet(fieldMask, DAY_OF_WEEK)) {
            firstDayOfWeek = BaseCalendar.getDayOfWeekDateOnOrBefore(firstDayOfWeek + 6,
                internalGet(DAY_OF_WEEK));
          }
          // In lenient mode, we treat days of the previous
          // months as a part of the specified
          // WEEK_OF_MONTH. See 4633646.
          fixedDate = firstDayOfWeek + 7 * (internalGet(WEEK_OF_MONTH) - 1);
        } else {
          int dayOfWeek;
          if (isFieldSet(fieldMask, DAY_OF_WEEK)) {
            dayOfWeek = internalGet(DAY_OF_WEEK);
          } else {
            dayOfWeek = getFirstDayOfWeek();
          }
          // We are basing this on the day-of-week-in-month.  The only
          // trickiness occurs if the day-of-week-in-month is
          // negative.
          int dowim;
          if (isFieldSet(fieldMask, DAY_OF_WEEK_IN_MONTH)) {
            dowim = internalGet(DAY_OF_WEEK_IN_MONTH);
          } else {
            dowim = 1;
          }
          if (dowim >= 0) {
            fixedDate = BaseCalendar.getDayOfWeekDateOnOrBefore(fixedDate + (7 * dowim) - 1,
                dayOfWeek);
          } else {
            // Go to the first day of the next week of
            // the specified week boundary.
            int lastDate = monthLength(month, year) + (7 * (dowim + 1));
            // Then, get the day of week date on or before the last date.
            fixedDate = BaseCalendar.getDayOfWeekDateOnOrBefore(fixedDate + lastDate - 1,
                dayOfWeek);
          }
        }
      }
    } else {
      if (year == gregorianCutoverYear && cal == gcal
          && fixedDate < gregorianCutoverDate
          && gregorianCutoverYear != gregorianCutoverYearJulian) {
        // January 1 of the year doesn't exist.  Use
        // gregorianCutoverDate as the first day of the
        // year.
        fixedDate = gregorianCutoverDate;
      }
      // We are on the first day of the year.
      if (isFieldSet(fieldMask, DAY_OF_YEAR)) {
        // Add the offset, then subtract 1. (Make sure to avoid underflow.)
        fixedDate += internalGet(DAY_OF_YEAR);
        fixedDate--;
      } else {
        long firstDayOfWeek = BaseCalendar.getDayOfWeekDateOnOrBefore(fixedDate + 6,
            getFirstDayOfWeek());
        // If we have enough days in the first week, then move
        // to the previous week.
        if ((firstDayOfWeek - fixedDate) >= getMinimalDaysInFirstWeek()) {
          firstDayOfWeek -= 7;
        }
        if (isFieldSet(fieldMask, DAY_OF_WEEK)) {
          int dayOfWeek = internalGet(DAY_OF_WEEK);
          if (dayOfWeek != getFirstDayOfWeek()) {
            firstDayOfWeek = BaseCalendar.getDayOfWeekDateOnOrBefore(firstDayOfWeek + 6,
                dayOfWeek);
          }
        }
        fixedDate = firstDayOfWeek + 7 * ((long) internalGet(WEEK_OF_YEAR) - 1);
      }
    }

    return fixedDate;
  }

  /**
   * Returns this object if it's normalized (all fields and time are
   * in sync). Otherwise, a cloned object is returned after calling
   * complete() in lenient mode.
   */
  private GregorianCalendar getNormalizedCalendar() {
    GregorianCalendar gc;
    if (isFullyNormalized()) {
      gc = this;
    } else {
      // Create a clone and normalize the calendar fields
      gc = (GregorianCalendar) this.clone();
      gc.setLenient(true);
      gc.complete();
    }
    return gc;
  }

  /**
   * Returns the Julian calendar system instance (singleton). 'jcal'
   * and 'jeras' are set upon the return.
   */
  private static synchronized BaseCalendar getJulianCalendarSystem() {
    if (jcal == null) {
      jcal = (JulianCalendar) CalendarSystem.forName("julian");
      jeras = jcal.getEras();
    }
    return jcal;
  }

  /**
   * Returns the calendar system for dates before the cutover date
   * in the cutover year. If the cutover date is January 1, the
   * method returns Gregorian. Otherwise, Julian.
   */
  private BaseCalendar getCutoverCalendarSystem() {
    if (gregorianCutoverYearJulian < gregorianCutoverYear) {
      return gcal;
    }
    return getJulianCalendarSystem();
  }

  /**
   * Determines if the specified year (normalized) is the Gregorian
   * cutover year. This object must have been normalized.
   */
  private boolean isCutoverYear(int normalizedYear) {
    int cutoverYear = (calsys == gcal) ? gregorianCutoverYear : gregorianCutoverYearJulian;
    return normalizedYear == cutoverYear;
  }

  /**
   * Returns the fixed date of the first day of the year (usually
   * January 1) before the specified date.
   *
   * @param date the date for which the first day of the year is calculated. The date has to be in
   * the cut-over year (Gregorian or Julian).
   * @param fixedDate the fixed date representation of the date
   */
  private long getFixedDateJan1(BaseCalendar.Date date, long fixedDate) {
    assert date.getNormalizedYear() == gregorianCutoverYear ||
        date.getNormalizedYear() == gregorianCutoverYearJulian;
    if (gregorianCutoverYear != gregorianCutoverYearJulian) {
      if (fixedDate >= gregorianCutoverDate) {
        // Dates before the cutover date don't exist
        // in the same (Gregorian) year. So, no
        // January 1 exists in the year. Use the
        // cutover date as the first day of the year.
        return gregorianCutoverDate;
      }
    }
    // January 1 of the normalized year should exist.
    BaseCalendar juliancal = getJulianCalendarSystem();
    return juliancal.getFixedDate(date.getNormalizedYear(), BaseCalendar.JANUARY, 1, null);
  }

  /**
   * Returns the fixed date of the first date of the month (usually
   * the 1st of the month) before the specified date.
   *
   * @param date the date for which the first day of the month is calculated. The date has to be in
   * the cut-over year (Gregorian or Julian).
   * @param fixedDate the fixed date representation of the date
   */
  private long getFixedDateMonth1(BaseCalendar.Date date, long fixedDate) {
    assert date.getNormalizedYear() == gregorianCutoverYear ||
        date.getNormalizedYear() == gregorianCutoverYearJulian;
    BaseCalendar.Date gCutover = getGregorianCutoverDate();
    if (gCutover.getMonth() == BaseCalendar.JANUARY
        && gCutover.getDayOfMonth() == 1) {
      // The cutover happened on January 1.
      return fixedDate - date.getDayOfMonth() + 1;
    }

    long fixedDateMonth1;
    // The cutover happened sometime during the year.
    if (date.getMonth() == gCutover.getMonth()) {
      // The cutover happened in the month.
      BaseCalendar.Date jLastDate = getLastJulianDate();
      if (gregorianCutoverYear == gregorianCutoverYearJulian
          && gCutover.getMonth() == jLastDate.getMonth()) {
        // The "gap" fits in the same month.
        fixedDateMonth1 = jcal.getFixedDate(date.getNormalizedYear(),
            date.getMonth(),
            1,
            null);
      } else {
        // Use the cutover date as the first day of the month.
        fixedDateMonth1 = gregorianCutoverDate;
      }
    } else {
      // The cutover happened before the month.
      fixedDateMonth1 = fixedDate - date.getDayOfMonth() + 1;
    }

    return fixedDateMonth1;
  }

  /**
   * Returns a CalendarDate produced from the specified fixed date.
   *
   * @param fd the fixed date
   */
  private BaseCalendar.Date getCalendarDate(long fd) {
    BaseCalendar cal = (fd >= gregorianCutoverDate) ? gcal : getJulianCalendarSystem();
    BaseCalendar.Date d = (BaseCalendar.Date) cal.newCalendarDate(TimeZone.NO_TIMEZONE);
    cal.getCalendarDateFromFixedDate(d, fd);
    return d;
  }

  /**
   * Returns the Gregorian cutover date as a BaseCalendar.Date. The
   * date is a Gregorian date.
   */
  private BaseCalendar.Date getGregorianCutoverDate() {
    return getCalendarDate(gregorianCutoverDate);
  }

  /**
   * Returns the day before the Gregorian cutover date as a
   * BaseCalendar.Date. The date is a Julian date.
   */
  private BaseCalendar.Date getLastJulianDate() {
    return getCalendarDate(gregorianCutoverDate - 1);
  }

  /**
   * Returns the length of the specified month in the specified
   * year. The year number must be normalized.
   *
   * @see #isLeapYear(int)
   */
  private int monthLength(int month, int year) {
    return isLeapYear(year) ? LEAP_MONTH_LENGTH[month] : MONTH_LENGTH[month];
  }

  /**
   * Returns the length of the specified month in the year provided
   * by internalGet(YEAR).
   *
   * @see #isLeapYear(int)
   */
  private int monthLength(int month) {
    int year = internalGet(YEAR);
    if (internalGetEra() == BCE) {
      year = 1 - year;
    }
    return monthLength(month, year);
  }

  private int actualMonthLength() {
    int year = cdate.getNormalizedYear();
    if (year != gregorianCutoverYear && year != gregorianCutoverYearJulian) {
      return calsys.getMonthLength(cdate);
    }
    BaseCalendar.Date date = (BaseCalendar.Date) cdate.clone();
    long fd = calsys.getFixedDate(date);
    long month1 = getFixedDateMonth1(date, fd);
    long next1 = month1 + calsys.getMonthLength(date);
    if (next1 < gregorianCutoverDate) {
      return (int) (next1 - month1);
    }
    if (cdate != gdate) {
      date = (BaseCalendar.Date) gcal.newCalendarDate(TimeZone.NO_TIMEZONE);
    }
    gcal.getCalendarDateFromFixedDate(date, next1);
    next1 = getFixedDateMonth1(date, next1);
    return (int) (next1 - month1);
  }

  /**
   * Returns the length (in days) of the specified year. The year
   * must be normalized.
   */
  private int yearLength(int year) {
    return isLeapYear(year) ? 366 : 365;
  }

  /**
   * Returns the length (in days) of the year provided by
   * internalGet(YEAR).
   */
  private int yearLength() {
    int year = internalGet(YEAR);
    if (internalGetEra() == BCE) {
      year = 1 - year;
    }
    return yearLength(year);
  }

  /**
   * After adjustments such as add(MONTH), add(YEAR), we don't want the
   * month to jump around.  E.g., we don't want Jan 31 + 1 month to go to Mar
   * 3, we want it to go to Feb 28.  Adjustments which might run into this
   * problem call this method to retain the proper month.
   */
  private void pinDayOfMonth() {
    int year = internalGet(YEAR);
    int monthLen;
    if (year > gregorianCutoverYear || year < gregorianCutoverYearJulian) {
      monthLen = monthLength(internalGet(MONTH));
    } else {
      GregorianCalendar gc = getNormalizedCalendar();
      monthLen = gc.getActualMaximum(DAY_OF_MONTH);
    }
    int dom = internalGet(DAY_OF_MONTH);
    if (dom > monthLen) {
      set(DAY_OF_MONTH, monthLen);
    }
  }

  /**
   * Returns the fixed date value of this object. The time value and
   * calendar fields must be in synch.
   */
  private long getCurrentFixedDate() {
    return (calsys == gcal) ? cachedFixedDate : calsys.getFixedDate(cdate);
  }

  /**
   * Returns the new value after 'roll'ing the specified value and amount.
   */
  private static int getRolledValue(int value, int amount, int min, int max) {
    assert value >= min && value <= max;
    int range = max - min + 1;
    amount %= range;
    int n = value + amount;
    if (n > max) {
      n -= range;
    } else if (n < min) {
      n += range;
    }
    assert n >= min && n <= max;
    return n;
  }

  /**
   * Returns the ERA.  We need a special method for this because the
   * default ERA is CE, but a zero (unset) ERA is BCE.
   */
  private int internalGetEra() {
    return isSet(ERA) ? internalGet(ERA) : CE;
  }

  /**
   * Updates internal state.
   */
  private void readObject(ObjectInputStream stream)
      throws IOException, ClassNotFoundException {
    stream.defaultReadObject();
    if (gdate == null) {
      gdate = (BaseCalendar.Date) gcal.newCalendarDate(getZone());
      cachedFixedDate = Long.MIN_VALUE;
    }
    setGregorianChange(gregorianCutover);
  }

  /**
   * Converts this object to a {@code ZonedDateTime} that represents
   * the same point on the time-line as this {@code GregorianCalendar}.
   * <p>
   * Since this object supports a Julian-Gregorian cutover date and
   * {@code ZonedDateTime} does not, it is possible that the resulting year,
   * month and day will have different values.  The result will represent the
   * correct date in the ISO calendar system, which will also be the same value
   * for Modified Julian Days.
   *
   * @return a zoned date-time representing the same point on the time-line as this gregorian
   * calendar
   * @since 1.8
   */
  public ZonedDateTime toZonedDateTime() {
    return ZonedDateTime.ofInstant(Instant.ofEpochMilli(getTimeInMillis()),
        getTimeZone().toZoneId());
  }

  /**
   * Obtains an instance of {@code GregorianCalendar} with the default locale
   * from a {@code ZonedDateTime} object.
   * <p>
   * Since {@code ZonedDateTime} does not support a Julian-Gregorian cutover
   * date and uses ISO calendar system, the return GregorianCalendar is a pure
   * Gregorian calendar and uses ISO 8601 standard for week definitions,
   * which has {@code MONDAY} as the {@link Calendar#getFirstDayOfWeek()
   * FirstDayOfWeek} and {@code 4} as the value of the
   * {@link Calendar#getMinimalDaysInFirstWeek() MinimalDaysInFirstWeek}.
   * <p>
   * {@code ZoneDateTime} can store points on the time-line further in the
   * future and further in the past than {@code GregorianCalendar}. In this
   * scenario, this method will throw an {@code IllegalArgumentException}
   * exception.
   *
   * @param zdt the zoned date-time object to convert
   * @return the gregorian calendar representing the same point on the time-line as the zoned
   * date-time provided
   * @throws NullPointerException if {@code zdt} is null
   * @throws IllegalArgumentException if the zoned date-time is too large to represent as a {@code
   * GregorianCalendar}
   * @since 1.8
   */
  public static GregorianCalendar from(ZonedDateTime zdt) {
    GregorianCalendar cal = new GregorianCalendar(TimeZone.getTimeZone(zdt.getZone()));
    cal.setGregorianChange(new Date(Long.MIN_VALUE));
    cal.setFirstDayOfWeek(MONDAY);
    cal.setMinimalDaysInFirstWeek(4);
    try {
      cal.setTimeInMillis(Math.addExact(Math.multiplyExact(zdt.toEpochSecond(), 1000),
          zdt.get(ChronoField.MILLI_OF_SECOND)));
    } catch (ArithmeticException ex) {
      throw new IllegalArgumentException(ex);
    }
    return cal;
  }
}
